CSLB HVAC (C-20) Trade — All Questions

In residential load calculations, what does an ACCA Manual J procedure primarily determine?

• a.The size and gauge of the supply ductwork
• b.The building's heating and cooling loads✓
• c.The refrigerant charge for the condenser
• d.The electrical service size for the panel

Manual J is the industry-standard residential load calculation method. It estimates the sensible and latent heating and cooling loads by accounting for construction, insulation, windows, orientation, infiltration, and local design temperatures. Equipment is then selected to match those calculated loads.California Energy Code (Title 24)

One ton of cooling capacity is equal to how many BTU per hour?

• a.6,000 BTU/hr
• b.9,000 BTU/hr
• c.12,000 BTU/hr✓
• d.15,000 BTU/hr

A ton of refrigeration equals 12,000 BTU/hr, derived from the heat needed to melt one ton of ice in 24 hours. This unit is the standard used to size air-conditioning and heat-pump equipment. A 3-ton system therefore provides about 36,000 BTU/hr of cooling.

A common rule-of-thumb airflow value for a residential cooling system is approximately how many CFM per ton?

• a.100 CFM per ton
• b.400 CFM per ton✓
• c.800 CFM per ton
• d.1,200 CFM per ton

Standard residential cooling airflow is roughly 400 CFM per ton, though it may range from 350 to 450 depending on climate and humidity. A 3-ton system therefore typically moves about 1,200 CFM. Correct airflow is essential for proper capacity and dehumidification.

A 4-ton air-conditioning system is designed at 400 CFM per ton. What total supply airflow is required?

• a.800 CFM
• b.1,200 CFM
• c.1,600 CFM✓
• d.2,000 CFM

Multiply tons by CFM per ton: 4 tons x 400 CFM = 1,600 CFM. Sizing the blower and ductwork for this airflow ensures the coil receives adequate air for rated capacity. Undersized ducts would restrict this airflow and reduce performance.

The sensible heat formula uses which constant when air volume is in CFM and temperature difference is in degrees F?

• a.0.68
• b.1.08✓
• c.4.5
• d.0.24

Sensible heat (BTU/hr) equals 1.08 x CFM x delta-T, where 1.08 combines air density, specific heat, and a time conversion. The 4.5 factor is used with enthalpy for total heat, and 0.68 is used for latent load with grains of moisture. These formulas let technicians verify airflow and capacity.

Using the sensible heat formula, how much sensible heat is removed when 1,200 CFM of air is cooled through a 20 degree F temperature drop?

• a.12,960 BTU/hr
• b.18,000 BTU/hr
• c.25,920 BTU/hr✓
• d.32,400 BTU/hr

Sensible heat = 1.08 x 1,200 CFM x 20 F = 25,920 BTU/hr. This calculation lets a technician confirm the coil is delivering close to its rated capacity. A result far below expected suggests low airflow or an undercharged system.

What does ACCA Manual D provide guidance for?

• a.Selecting the correct condenser
• b.Sizing and designing residential duct systems✓
• c.Calculating building heat loss
• d.Selecting the proper thermostat

Manual D is the ACCA standard for residential duct design. It uses the available static pressure and required airflow to size trunks, branches, and fittings so each room receives its design CFM. Proper duct design prevents noise, high static pressure, and uneven comfort.

After a Manual J load is calculated, which ACCA procedure is used to select the specific equipment model?

• a.Manual D
• b.Manual T
• c.Manual S✓
• d.Manual RS

Manual S matches equipment to the Manual J loads using manufacturer expanded performance data at local design conditions. It ensures the unit meets both sensible and latent loads without gross oversizing. Oversized equipment short-cycles and dehumidifies poorly.

Oversizing a residential air conditioner most commonly leads to which problem?

• a.Higher heating capacity
• b.Short cycling and poor humidity control✓
• c.Lower refrigerant pressures
• d.Reduced supply air temperature

An oversized unit cools the air quickly and satisfies the thermostat before it runs long enough to remove moisture, causing short cycling. The result is a cool but clammy space and increased wear from frequent starts. Correct sizing from Manual J and S avoids this.

Which factor increases a building's cooling load the most on a hot afternoon?

• a.Large west-facing glass in direct afternoon sun✓
• b.North-facing walls with continuous insulation
• c.A well-sealed and insulated attic hatch
• d.Low-wattage LED lighting in the ceilings

West-facing windows receive intense direct solar radiation in the afternoon, adding substantial sensible heat gain. This solar load is often a dominant component of the peak cooling load. Shading and low-SHGC glazing reduce this gain.

In California, plans for new HVAC systems typically must demonstrate compliance with which energy standard?

• a.The National Electrical Code
• b.Title 24, Part 6 energy efficiency standards✓
• c.The Uniform Plumbing Code
• d.The Americans with Disabilities Act

Title 24, Part 6 sets California's building energy efficiency standards, including HVAC equipment efficiency, duct sealing, and refrigerant charge verification. New and altered systems generally must show compliance through prescriptive or performance methods. Documentation is submitted with the permit application.California Energy Code (Title 24)

Under the California Mechanical Code, when is a permit generally required for HVAC work?

• a.Only for work in commercial or industrial buildings
• b.Only when a thermostat is being replaced
• c.When equipment is installed, altered, or replaced✓
• d.Only for gas-fired appliances such as furnaces

The CMC and local jurisdictions require a mechanical permit for installing, altering, or replacing regulated equipment like furnaces, air conditioners, and ductwork. Permits trigger inspection to verify code-compliant, safe installation. Minor maintenance such as filter changes does not require a permit.2022 California Mechanical Code (CMC)

What is the primary purpose of a Manual J block load versus a room-by-room load?

• a.To size the refrigerant liquid and suction lines
• b.To set the total equipment capacity for the house✓
• c.To determine the required duct insulation value
• d.To calculate the gas meter and pipe sizes

A block (whole-house) load establishes the total heating and cooling capacity the equipment must provide. A room-by-room load then distributes that capacity to size individual ducts and registers. Both are needed for a complete design.

If a home has a calculated cooling load of 30,000 BTU/hr, what nominal equipment size is the closest match?

• a.2 tons
• b.2.5 tons✓
• c.3.5 tons
• d.4 tons

30,000 BTU/hr divided by 12,000 BTU/hr per ton equals 2.5 tons. Manual S guides selecting a unit whose capacity at design conditions closely matches this load. Choosing 2.5 tons avoids the humidity and cycling problems of oversizing.

Friction rate in duct design is typically expressed in which units?

• a.CFM per square foot of floor area served
• b.BTU per hour per square foot of duct
• c.Inches of water column per 100 feet of duct✓
• d.Feet per minute per 100 feet of duct

Friction rate expresses the pressure loss per unit length of duct, in inches of water column per 100 feet. In Manual D, the available static pressure and total effective length set the design friction rate used to size ducts. A higher friction rate yields smaller, higher-velocity ducts.

Air velocity in a duct is calculated by dividing airflow (CFM) by what?

• a.The total length of the duct run in feet
• b.The cross-sectional area of the duct in square feet✓
• c.The static pressure in the duct in inches w.c.
• d.The temperature difference across the coil in F

Velocity in feet per minute equals CFM divided by the duct cross-sectional area in square feet. Excessive velocity causes noise and high friction losses, while too little velocity can reduce throw and mixing. Designers balance velocity against static pressure limits.

A branch duct must deliver 200 CFM at a velocity of about 600 feet per minute. Approximately what free area is required?

• a.0.10 square feet
• b.0.20 square feet
• c.0.33 square feet✓
• d.0.66 square feet

Area equals CFM divided by velocity: 200 / 600 = 0.33 square feet. This corresponds to roughly a 8-inch round duct. Selecting the right size keeps velocity and noise within acceptable limits.

Under California energy standards, duct leakage in many new and altered systems must be verified by which method?

• a.Visual inspection of accessible duct joints
• b.A duct leakage test under pressurization✓
• c.A refrigerant charge verification test
• d.A combustion analysis of the furnace

Title 24 requires duct leakage testing for many new installations and changeouts, typically verified through a pressurization test. Sealing ducts reduces energy waste and improves delivered airflow. Results are often confirmed by a HERS rater.California Energy Code (Title 24)

Which condition would a technician correct by performing an accurate load calculation instead of using a rule of thumb like square footage per ton?

• a.Comfort complaints from badly sized equipment✓
• b.A dirty condenser coil that restricts airflow
• c.A tripped condensate float switch
• d.A failed compressor run capacitor

Square-foot rules of thumb ignore insulation, glazing, orientation, and infiltration, often producing oversized or undersized equipment and comfort complaints. A Manual J load accounts for these variables and yields correctly sized equipment. This is the proper professional approach.

Latent load in a cooling calculation refers to the energy required to do what?

• a.Raise the dry-bulb temperature of the air
• b.Remove moisture (water vapor) from the air✓
• c.Overcome duct friction
• d.Power the compressor motor

Latent load is the heat associated with condensing water vapor out of the air, lowering humidity. Sensible load changes air temperature, while latent load changes moisture content. Both must be met for comfort, especially in humid climates.

A 3-ton system is selected for a home. At 400 CFM per ton, what is the target blower airflow?

• a.800 CFM
• b.1,000 CFM
• c.1,200 CFM✓
• d.1,500 CFM

3 tons x 400 CFM per ton = 1,200 CFM. The blower and duct system should be configured to deliver this airflow at the system's external static pressure. Verifying actual airflow after installation confirms proper capacity.

What is the main benefit of properly sizing equipment to a load calculation rather than oversizing?

• a.Faster refrigerant charging during start-up
• b.Better humidity control, comfort, and efficiency✓
• c.Elimination of the mechanical permit
• d.Higher supply air velocity at the registers

Right-sized equipment runs longer, steadier cycles that dehumidify effectively and hold temperature evenly, improving comfort and efficiency. Oversizing wastes energy through short cycling and leaves the space humid. This aligns with Title 24 efficiency goals.California Energy Code (Title 24)

What is the primary purpose of providing combustion air to a gas-fired furnace?

• a.To cool the furnace electronic control board
• b.To supply oxygen for complete, safe combustion✓
• c.To raise the supply air temperature further
• d.To reduce refrigerant head pressure

A gas furnace needs adequate combustion air so the burner receives enough oxygen for complete combustion. Insufficient air causes incomplete combustion, producing carbon monoxide and sooting. The CMC specifies required openings or ducts based on the appliance input and the confining space.2022 California Mechanical Code (CMC)

When two combustion-air openings are used for an appliance in a confined space communicating with outdoors, they are generally located how?

• a.Both openings near the floor of the confined space
• b.Both openings in the ceiling of the space
• c.One opening near the top, one near the bottom✓
• d.One opening in an interior wall only

Two openings, one high and one low, allow both makeup combustion air and ventilation of heat. The high opening relieves warm air while the low opening supplies denser cooler air. The CMC sizes each opening based on appliance input and whether air comes from indoors or outdoors.2022 California Mechanical Code (CMC)

Type B gas vent is designed to vent the products of combustion from which appliances?

• a.Oil-fired appliances fitted with barometric dampers
• b.Listed Category I gas appliances with draft hoods✓
• c.Solid-fuel wood stoves and fireplaces
• d.High-temperature incinerators and boilers

Type B vent is a double-wall metal vent listed for venting listed gas appliances that produce relatively low-temperature, non-condensing flue gases, such as Category I furnaces. It must not be used with appliances that produce condensing or high-temperature flue products. Proper vent selection is required by the CMC.2022 California Mechanical Code (CMC)

A high-efficiency condensing furnace (Category IV) is typically vented with what material?

• a.Type B double-wall metal vent
• b.Single-wall galvanized pipe
• c.Listed PVC or CPVC plastic pipe✓
• d.Masonry chimney only

Condensing furnaces cool flue gases below their dew point, producing acidic condensate and low-temperature exhaust, so they are vented with listed plastic pipe such as PVC or CPVC. Metal Type B vent would corrode and is not rated for positive-pressure condensing appliances. Manufacturer instructions specify approved materials and lengths.2022 California Mechanical Code (CMC)

Why must condensate from a condensing furnace or cooling coil be routed to an approved drain?

• a.To increase the cooling system's rated efficiency
• b.To prevent water damage and drain condensate safely✓
• c.To raise the refrigerant subcooling value
• d.To supply combustion air to the burners

Cooling coils and condensing furnaces generate liquid condensate that must drain to an approved location to prevent overflow, water damage, and microbial growth. The CMC requires proper slope, trapping where needed, and a secondary drain or float switch in many installations. Improper drainage is a common cause of ceiling damage.2022 California Mechanical Code (CMC)

A secondary condensate drain pan or float switch is typically required when an air handler is installed where?

• a.In a detached garage on a concrete slab
• b.In a basement served by a floor drain
• c.In an attic above a finished ceiling✓
• d.On a ground-level slab outdoors

When an air handler is located above a finished space, such as in an attic, code requires a secondary means of protection like an auxiliary drain pan or a float switch. These devices catch or shut off the system if the primary drain clogs. This prevents costly water damage to ceilings below.2022 California Mechanical Code (CMC)

When brazing refrigerant copper line sets, dry nitrogen is flowed through the tubing to accomplish what?

• a.Add the initial refrigerant charge to the lines
• b.Prevent oxide scale forming inside the tubing✓
• c.Raise the temperature of the brazed joint
• d.Test the thermostat and control wiring

Flowing a small amount of dry nitrogen through the lines during brazing displaces oxygen and prevents the formation of copper oxide scale inside the tubing. That scale can break loose and clog metering devices or contaminate the system. This practice protects the refrigerant circuit.

Refrigerant suction lines on a split system are typically insulated for what reason?

• a.To add structural support to the line set
• b.To prevent refrigerant from leaking at joints
• c.To limit heat gain and prevent condensation✓
• d.To increase the pressure in the suction line

The suction line carries cold, low-pressure vapor, so it is insulated to limit heat gain that would reduce efficiency and to prevent surface condensation that drips and causes damage. The insulation should be continuous and properly sized. The liquid line is usually left uninsulated unless exposed to extreme heat.

What is the purpose of maintaining manufacturer-specified clearances to combustibles around a furnace?

• a.To improve static pressure measurement at the coil
• b.To keep nearby combustible materials from igniting✓
• c.To lower the refrigerant charge in the system
• d.To allow the ductwork to expand and contract

Listed clearances to combustibles ensure the heat radiating from the furnace and vent does not ignite nearby wood, drywall paper, or stored materials. These clearances are set by the appliance listing and the CMC. Maintaining them and service access is required for safe operation.2022 California Mechanical Code (CMC)

A properly installed refrigerant line set should have the liquid line and suction line sized according to what?

• a.The color coding of the line-set insulation jacket
• b.The length of the thermostat control wiring
• c.Manufacturer tables for capacity and line length✓
• d.The size of the electrical branch breaker

Line-set diameters are selected from manufacturer tables based on system tonnage, total line length, and vertical rise. Incorrect sizing causes oil-return problems, capacity loss, or excessive pressure drop. Following the specifications ensures proper refrigerant and oil flow.

On a long vertical suction riser, what feature helps ensure compressor oil returns properly?

• a.A deeper condensate trap at the indoor air handler
• b.Line sizing that maintains refrigerant velocity✓
• c.Extra thermostat wire coiled at the unit
• d.A larger return-air filter at the grille

Oil circulates with the refrigerant and must be carried back to the compressor by adequate vapor velocity, especially in vertical suction risers. If the line is oversized, velocity drops and oil pools, starving the compressor of lubrication. Proper sizing, and traps where required by the manufacturer, maintain oil return.

In a split-system heat pump, the outdoor coil functions as the condenser during which mode?

• a.Heating mode
• b.Defrost mode
• c.Cooling mode✓
• d.Emergency heat mode

In cooling mode the outdoor coil rejects heat and acts as the condenser, while the indoor coil absorbs heat as the evaporator. In heating mode the reversing valve swaps these roles. Understanding this reversal is key to installing and servicing heat pumps.

What is the function of the reversing valve in a heat pump?

• a.To meter liquid refrigerant into the evaporator coil
• b.To reverse refrigerant flow for heating or cooling✓
• c.To drain condensate from the outdoor coil pan
• d.To regulate the gas pressure at the burners

The reversing valve redirects refrigerant flow so the same equipment can both heat and cool by switching which coil is the condenser and which is the evaporator. It is energized or de-energized depending on the manufacturer's design. A stuck valve is a common heat-pump service issue.

A package unit differs from a split system in what way?

• a.It operates without any compressor or fan
• b.It can provide heating but never cooling
• c.All major components sit in one cabinet✓
• d.It connects to the building without ductwork

In a packaged unit the compressor, condenser, evaporator, and blower are housed in one cabinet, usually on a roof or slab, connected to the building by ductwork. A split system separates the indoor and outdoor sections and connects them with a refrigerant line set. Each configuration has different installation requirements.

Gas piping for a furnace must be sized primarily to do what?

• a.Match the diameter of the refrigerant lines
• b.Deliver enough gas at the required pressure✓
• c.Reduce the electrical load on the circuit
• d.Support the weight of the condensate drain

Gas pipe is sized from tables using the appliance input in BTU/hr, the pipe length, and the allowable pressure drop so every appliance receives adequate fuel. Undersized piping starves burners and causes poor combustion. The CMC provides sizing tables and requirements.2022 California Mechanical Code (CMC)

What is the purpose of a sediment trap (drip leg) installed near a gas appliance?

• a.To regulate the gas pressure delivered to the burners
• b.To vent excess gas from the supply line
• c.To catch moisture and debris before the gas valve✓
• d.To measure the gas flow to the appliance

A sediment trap, or drip leg, is a short vertical section that captures moisture, rust, and debris carried in the gas stream before they reach the appliance gas valve. This protects the valve and burner orifices from clogging. The CMC requires it on many appliance connections.2022 California Mechanical Code (CMC)

Before a new furnace's electrical connections are energized, the technician should verify what first?

• a.That condensate is flowing from the drain pan
• b.Correct voltage, polarity, and grounding✓
• c.The refrigerant subcooling at the liquid line
• d.The R-value of the supply duct insulation

Verifying supply voltage, proper polarity, and a secure ground before energizing protects the equipment controls and the technician. Loose or reversed connections can damage the board or create a shock hazard. The unit's wiring diagram and nameplate provide the required values.

Flexible duct connectors at the air handler are commonly used to accomplish what?

• a.Increase static pressure at the blower outlet
• b.Filter the supply air leaving the cabinet
• c.Reduce vibration and noise entering the ducts✓
• d.Add refrigerant capacity to the coil

A flexible canvas or fabric connector between the unit and rigid ductwork isolates blower vibration and reduces noise transmitted into the structure. It also accommodates slight misalignment. It must be installed without restricting airflow.

Why should supply and return ducts be sealed with mastic or listed tape at joints?

• a.To increase the gas supply pressure at the burner
• b.To stop leakage that wastes energy and airflow✓
• c.To hold refrigerant inside the duct system
• d.To help support the weight of the furnace

Sealing duct joints with mastic or UL-listed tape prevents conditioned air from leaking into unconditioned spaces, which wastes energy and starves rooms of airflow. Leaky returns can also draw in dust or combustion products. California energy standards require duct sealing and testing.

When installing a split-system condenser, adequate clearance around the unit is needed mainly to ensure what?

• a.Lower electrical consumption by the compressor motor
• b.Use of the correct refrigerant type and charge
• c.Free airflow across the coil and service access✓
• d.Shorter thermostat wire runs to the outdoor unit

The condenser must draw ambient air freely across its coil to reject heat; obstructions raise head pressure and cut capacity. Clearance also allows access for service and maintenance. Manufacturer instructions specify minimum distances from walls and other units.

A furnace installed in an upflow configuration discharges heated air in which direction?

• a.Downward through the bottom
• b.Upward through the top of the cabinet✓
• c.Horizontally to the side
• d.Directly outdoors

An upflow furnace pulls return air in at the bottom and discharges heated supply air out the top, typical for basement or closet installations with overhead ductwork. Downflow and horizontal furnaces are oriented for other duct arrangements. The airflow direction must match the duct layout.

A furnace located in an attic generally requires what for code-compliant service?

• a.No special access provisions are needed
• b.A refrigerant recovery machine on site
• c.A passageway, work platform, and light✓
• d.A second gas meter at the appliance

The CMC requires attic-installed appliances to have a solid passageway to the unit, a level service platform in front of it, and a light with a switch for safe servicing. These provisions protect technicians and allow proper maintenance. Access dimensions are specified in the code.2022 California Mechanical Code (CMC)

The condensate drain line from a cooling coil is often fitted with a trap to accomplish what?

• a.Add refrigerant to the evaporator coil
• b.Stop air being pulled through the drain✓
• c.Increase the blower speed at the coil
• d.Filter the return air entering the unit

A properly sized trap on a draw-through coil prevents the blower's negative pressure from either holding water in the pan or pulling air backward through the drain. This allows condensate to flow freely to the drain. The trap depth is based on the unit's static pressure.

What is the recommended practice for supporting horizontal refrigerant and drain lines?

• a.Leave the lines unsupported between fittings
• b.Support the lines only at the equipment
• c.Support at intervals to prevent sagging✓
• d.Bury the lines without any protection

Adequate, evenly spaced supports keep refrigerant lines from sagging and vibrating and maintain the continuous downward slope required for condensate drainage. Sagging drain lines create traps that hold water and cause overflow. Support intervals follow manufacturer and code guidance.

Before releasing refrigerant charge into a newly installed line set, the system should be tested and then processed how?

• a.Charged immediately without any leak or vacuum test
• b.Pressure tested, then evacuated to a deep vacuum✓
• c.Filled with water and drained before charging
• d.Left open to the atmosphere overnight

Best practice is to pressure test the assembled line set for leaks, then pull a deep vacuum to remove moisture and non-condensable gases before charging. Moisture left inside can freeze at the metering device and form acids. Only after a proper evacuation should refrigerant be introduced.

A gas furnace flue must terminate where?

• a.Inside the attic space above the furnace
• b.Into an open, ventilated crawl space
• c.Outdoors with the required clearances✓
• d.Into the return duct near the blower

Flue and vent terminations must discharge outdoors at listed heights and clearances from windows, doors, and air intakes to prevent flue gases from re-entering the building. The CMC and appliance listing specify these termination requirements. Improper termination risks carbon monoxide entry.2022 California Mechanical Code (CMC)

When connecting line-voltage power to an air conditioner, the disconnect switch must be located where?

• a.Inside the main electrical panel only
• b.Within sight of the outdoor unit✓
• c.In the attic above the air handler
• d.Behind the condenser coil guard

A readily accessible disconnecting means within sight of the outdoor unit allows a technician to safely de-energize the equipment for service. This is both a code requirement and a safety best practice. The disconnect is sized for the unit's electrical load.

What is the purpose of a filter drier installed in the liquid line?

• a.To meter refrigerant into the evaporator
• b.To insulate the liquid line from heat
• c.To remove moisture and trap contaminants✓
• d.To increase the suction line pressure

A liquid-line filter drier adsorbs moisture and captures particulate contaminants, protecting the metering device and compressor. It is typically replaced whenever the system is opened for major service. A saturated drier can restrict flow and should be changed.

Return air for a gas furnace must not be taken from which location?

• a.A hallway serving several bedrooms
• b.A garage or space with combustion byproducts✓
• c.A conditioned bedroom with its own return grille
• d.A central living room with a high ceiling

Drawing return air from a garage, furnace room, or similar space risks pulling in carbon monoxide, fuel vapors, or other contaminants and distributing them through the home. The CMC prohibits return openings in these locations. Return air must come from conditioned, safe spaces.2022 California Mechanical Code (CMC)

When mounting an outdoor condenser on a slab, the pad should be installed how?

• a.Sloped steeply back toward the building wall
• b.Level, on a stable base off the ground✓
• c.Directly on loose, uncompacted soil
• d.Tilted so that condensate pools beneath it

The condenser pad should be level and set on a firm, stable base so the unit sits securely and drains properly, avoiding settling that stresses the line set. A level unit also ensures correct oil return and fan operation. The pad keeps the cabinet off wet ground and debris.

In the basic refrigeration cycle, which component absorbs heat from the conditioned space?

• a.The condenser
• b.The evaporator✓
• c.The compressor
• d.The metering device

The evaporator is where low-pressure liquid refrigerant boils and absorbs heat from the indoor air, cooling the space. The condenser then rejects that heat outdoors. This heat-absorption step is the cooling effect of the system.

What is the primary function of the compressor in the refrigeration cycle?

• a.To absorb heat from the conditioned space
• b.To meter refrigerant into the evaporator coil
• c.To raise vapor pressure and circulate it✓
• d.To drain condensate from the indoor coil

The compressor draws in low-pressure vapor from the evaporator and compresses it to a high pressure and temperature, then discharges it to the condenser. This pressure difference drives refrigerant flow around the loop. It is often called the heart of the system.

The condenser in an air-conditioning system performs which function?

• a.Absorbs heat and boils liquid refrigerant
• b.Rejects heat and condenses vapor to liquid✓
• c.Meters refrigerant flow into the coil
• d.Filters particles from the supply air

In the condenser, high-pressure, high-temperature vapor gives up heat to the outdoor air and condenses into a high-pressure liquid. This heat rejection is what allows the cycle to remove heat from indoors. Airflow across the condenser coil is essential for this process.

A thermostatic expansion valve (TXV) controls refrigerant flow into the evaporator to maintain what?

• a.Constant condenser pressure
• b.Constant compressor speed
• c.A relatively constant evaporator superheat✓
• d.Constant subcooling

A TXV modulates refrigerant flow to hold a stable superheat at the evaporator outlet, matching flow to the load. This keeps the coil fed efficiently and protects the compressor from liquid floodback. It responds to the temperature and pressure of the suction line.

Superheat is defined as the temperature of the refrigerant vapor above what?

• a.Its condensing temperature at high side pressure
• b.Its saturation temperature at the existing pressure✓
• c.The outdoor ambient dry-bulb temperature
• d.The compressor discharge line temperature

Superheat is the number of degrees the refrigerant vapor has been heated above its saturation temperature for the measured pressure. Adequate superheat ensures only vapor, not liquid, returns to the compressor. Technicians measure it to evaluate evaporator charge and load.

A technician measures a suction pressure whose saturation temperature is 40 F and a suction line temperature of 52 F. What is the superheat?

• a.4 degrees
• b.8 degrees
• c.12 degrees✓
• d.20 degrees

Superheat equals the suction line temperature minus the saturation temperature: 52 F minus 40 F equals 12 degrees. This value helps confirm proper evaporator feeding and charge. Very low superheat risks liquid floodback, while very high superheat suggests underfeeding.

Subcooling is measured at which point in the system?

• a.At the evaporator outlet
• b.At the condenser outlet (liquid line)✓
• c.At the compressor suction
• d.At the filter on the return duct

Subcooling is measured at the condenser outlet by comparing the liquid line temperature to the saturation temperature for the high-side pressure. It indicates how much the liquid has cooled below its condensing point. Subcooling is a primary charging check on TXV systems.

On a system with a condensing saturation temperature of 105 F and a liquid line temperature of 95 F, what is the subcooling?

• a.5 degrees
• b.8 degrees
• c.10 degrees✓
• d.15 degrees

Subcooling equals the saturation temperature minus the liquid line temperature: 105 F minus 95 F equals 10 degrees. This is a typical target range for many TXV systems. Low subcooling can indicate an undercharge, while high subcooling can indicate an overcharge or restriction.

On a fixed-orifice (piston) system, which method is generally used to check the charge?

• a.The subcooling method with a PT chart
• b.The superheat method with a target chart✓
• c.Weighing the compressor oil charge
• d.Measuring external static pressure

Fixed-orifice metering devices are charged by the superheat method, comparing measured superheat to a target based on indoor wet-bulb and outdoor dry-bulb temperatures. TXV systems, by contrast, are typically charged by subcooling. Using the correct method for the metering device is essential.

Under EPA Section 608, what must a technician do with refrigerant before opening most systems for service?

• a.Vent it slowly to the atmosphere
• b.Mix it with dry nitrogen first
• c.Recover it with certified equipment✓
• d.Burn it off with a torch flame

Section 608 prohibits knowingly venting most refrigerants and requires recovery into approved equipment before opening a system. This protects the atmosphere and conserves refrigerant. Only certified technicians using certified equipment may perform this work.EPA Section 608

EPA Section 608 certification is required for technicians who do what?

• a.Install sheet-metal ductwork and register boots
• b.Service or dispose of refrigerant equipment✓
• c.Wire thermostats and control circuits
• d.Design residential duct systems only

Section 608 requires certification for anyone who could release ozone-depleting or certain other regulated refrigerants during service, maintenance, repair, or disposal. Different certification types cover small appliances, high-pressure, and low-pressure systems. Working with refrigerant without certification is a violation.EPA Section 608

Evacuating a system with a vacuum pump primarily removes what?

• a.Refrigerant oil from the compressor sump
• b.Copper oxide scale from inside the tubing
• c.Moisture and non-condensable gases like air✓
• d.Varnish from the compressor windings

A deep vacuum boils off moisture and pulls out air and other non-condensables that would otherwise raise head pressure, form acids, or cause icing at the metering device. A micron gauge verifies the target vacuum is reached and held. Proper evacuation is essential before charging.

A micron gauge is used during evacuation to measure what?

• a.Refrigerant weight
• b.The depth of vacuum in the system✓
• c.Superheat
• d.Airflow

A micron gauge measures the absolute pressure (depth of vacuum) far more precisely than a compound gauge, confirming that the system is dry and tight. Technicians pull the system down to a target micron level and perform a decay test. Failure to hold vacuum indicates moisture or a leak.

Which instrument or method is commonly used for pinpointing small refrigerant leaks?

• a.A megohmmeter connected across the windings
• b.A manometer connected to the coil
• c.An electronic detector or bubble solution✓
• d.A pyrometer clamped to the line

Electronic leak detectors sense refrigerant escaping at joints, and bubble solutions reveal leaks visibly. Ultraviolet dye is another method for hard-to-find leaks. Locating and repairing leaks is required before recharging a system.

As a general principle, adding refrigerant charge to a properly running system tends to do what to the low-side pressure?

• a.Lower it significantly
• b.Raise it✓
• c.Have no effect
• d.Reverse compressor rotation

Adding charge generally raises system pressures, including the suction (low-side) pressure, while removing charge lowers them. Technicians interpret these trends together with superheat and subcooling. Charging must be verified against manufacturer targets, not pressure alone.

A refrigerant metering device such as a fixed orifice or TXV creates what effect on the refrigerant?

• a.Raises its pressure before the condenser
• b.Condenses it fully into a liquid
• c.Drops its pressure so it boils cold✓
• d.Superheats the vapor before the condenser

The metering device restricts flow, dropping the high-pressure liquid to a low pressure so it can boil at a low temperature and absorb heat in the evaporator. This division between high and low sides is central to the cycle. TXVs also modulate this flow to control superheat.

Which category of refrigerants is being phased down under regulations due to high global warming potential?

• a.Water-based refrigerants
• b.Many high-GWP HFC refrigerants✓
• c.Nitrogen
• d.Carbon dioxide only

Regulations at the federal and California level are phasing down high global-warming-potential HFC refrigerants in favor of lower-GWP alternatives. Technicians must stay current on approved refrigerants and handling rules. Recovery and reclamation remain required under Section 608.EPA Section 608

A compressor that is trying to compress liquid refrigerant returning from the evaporator can suffer what damage?

• a.Improved efficiency and lower head pressure
• b.Higher superheat at the compressor inlet
• c.Slugging that damages valves or bearings✓
• d.Lower amp draw at the compressor terminals

Liquid refrigerant is nearly incompressible, so liquid floodback or slugging can damage compressor valves, bearings, and rods. Maintaining adequate superheat prevents liquid from reaching the compressor. This is why superheat is carefully controlled.

When comparing the two sides of an operating system, the discharge line is normally which relative to the suction line?

• a.Colder and lower pressure
• b.Hotter and higher pressure✓
• c.The same temperature and pressure
• d.Filled only with liquid

The discharge line leaving the compressor carries high-pressure, high-temperature vapor, while the suction line carries low-pressure, cooler vapor returning to the compressor. Recognizing these normal conditions helps a technician diagnose faults. Abnormal readings point to charge or airflow problems.

A reciprocating compressor changes the refrigerant state by doing what?

• a.Condensing the high-pressure vapor into liquid
• b.Metering liquid flow into the evaporator
• c.Compressing low-pressure vapor with pistons✓
• d.Boiling liquid refrigerant in the coil

A reciprocating compressor uses pistons driven by a crankshaft to draw in and compress refrigerant vapor, raising its pressure and temperature. Scroll and rotary compressors accomplish the same result by different mechanisms. The compressor circulates refrigerant and establishes the high and low sides.

High condenser (head) pressure with normal charge is most often caused by what?

• a.Overcharged suction line insulation
• b.Poor airflow or a dirty condenser coil✓
• c.A shorted thermostat
• d.An oversized return grille

Restricted condenser airflow, from a dirty coil, failing fan, or blocked clearance, prevents adequate heat rejection and raises head pressure. Non-condensables or overcharge can also raise head pressure. Cleaning the coil and confirming fan operation are first steps.

The saturation temperature corresponding to a measured pressure is found using what?

• a.The equipment nameplate data plate
• b.A duct calculator or sizing wheel
• c.A pressure-temperature chart or app✓
• d.The unit's electrical wiring schematic

A pressure-temperature chart lists the saturation temperature for each pressure of a given refrigerant. Technicians use it to calculate superheat and subcooling from gauge readings. Each refrigerant has its own PT relationship, so the correct chart must be used.

What is the primary function of a run capacitor on a single-phase motor?

• a.To fuse and protect the motor branch circuit
• b.To provide a phase shift for smooth running✓
• c.To ground the motor frame to the cabinet
• d.To measure airflow through the blower

A run capacitor stays in the circuit during operation, creating the phase shift the motor needs for efficient torque and smoother running. A weak or failed run capacitor causes low torque, overheating, and high amp draw. It is tested with a capacitance meter against its microfarad rating.

A start capacitor differs from a run capacitor in that it is designed to do what?

• a.Stay energized continuously while running
• b.Regulate refrigerant flow to the coil
• c.Give a brief torque boost, then drop out✓
• d.Filter the supply air leaving the unit

A start capacitor provides a large capacitance boost to start a motor under load and is switched out by a relay once the motor is up to speed. It is not rated for continuous duty. It is used with hard-start kits and certain compressor and motor designs.

A contactor in an air-conditioning condenser performs what function?

• a.Meters refrigerant flow into the evaporator
• b.Switches line voltage to the compressor✓
• c.Drains condensate from the coil pan
• d.Adjusts the indoor blower motor speed

The contactor is an electrically operated switch whose coil is energized by the low-voltage control circuit, closing contacts that supply line voltage to the compressor and condenser fan. Pitted or welded contacts are a common failure. It is tested for coil continuity and contact condition.

A typical low-voltage control (thermostat) circuit in residential HVAC operates at what voltage?

• a.120 volts
• b.240 volts
• c.24 volts✓
• d.480 volts

Residential control circuits generally operate at 24 volts AC, supplied by a step-down transformer. The thermostat switches this low voltage to energize relays and contactors. Measuring 24 volts at the appropriate terminals helps confirm control-circuit operation.

If a condenser fan motor fails while the compressor keeps running, what symptom is most likely?

• a.Low head pressure and high subcooling
• b.Rising head pressure and an overload trip✓
• c.Increased subcooling with normal pressures
• d.Lower amp draw on the compressor motor

Without condenser airflow, heat rejection collapses and head pressure climbs quickly, often tripping a high-pressure switch or the compressor overload. The system may also lose capacity and overheat. Diagnosing a hot, non-spinning fan points to the motor or its capacitor.

Low airflow across an evaporator coil during cooling most commonly causes what?

• a.High superheat measured at the coil outlet
• b.Higher supply air temperature at registers
• c.A cold or frozen coil and low suction pressure✓
• d.Higher airflow across the condenser coil

Restricted evaporator airflow, from a dirty filter, blocked coil, or weak blower, reduces heat pickup so the coil runs colder and suction pressure drops, sometimes freezing the coil. Restoring airflow by cleaning filters and coils is the first corrective step. A frozen coil should be thawed before further diagnosis.

SEER (or SEER2) is a rating that describes what?

• a.The seasonal heating efficiency of a gas furnace
• b.Seasonal cooling efficiency of the equipment✓
• c.The refrigerant type used in the system
• d.The measured duct leakage rate at test

SEER, and the updated SEER2, express the seasonal cooling output divided by the electrical energy input, so a higher number means greater cooling efficiency. It is used to compare and select air conditioners and heat pumps. California energy standards set minimum SEER values.

AFUE is the efficiency rating used for what equipment?

• a.Air conditioners
• b.Cooling towers
• c.Gas and oil furnaces✓
• d.Duct systems

Annual Fuel Utilization Efficiency (AFUE) expresses the percentage of fuel energy a furnace converts to usable heat over a season. A 95 percent AFUE furnace delivers 95 percent of the fuel's energy as heat. It is the standard heating-efficiency metric for furnaces.

HSPF (or HSPF2) rates the seasonal efficiency of what?

• a.A gas furnace
• b.A heat pump in heating mode✓
• c.An evaporative cooler
• d.A duct booster fan

Heating Seasonal Performance Factor rates how efficiently a heat pump delivers heat over a heating season. A higher HSPF, or the updated HSPF2, means more heat per unit of electricity. It complements SEER, which rates the same unit's cooling efficiency.

A furnace that heats briefly then shuts off repeatedly before satisfying the thermostat is exhibiting what?

• a.Normal operation
• b.A refrigerant leak
• c.Short cycling✓
• d.High subcooling

Short cycling is repeated brief on-off operation before the space reaches setpoint, often caused by an overheating limit trip, a dirty flame sensor, oversizing, or restricted airflow. It wastes energy and stresses components. Diagnosis targets airflow, the limit switch, and flame sensing.

A dirty flame sensor on a modern furnace most commonly causes what symptom?

• a.The system runs in continuous cooling mode
• b.The burners light, then shut off in seconds✓
• c.The compressor runs at very high head pressure
• d.The evaporator coil freezes over solid

A flame sensor confirms flame is present; when it is coated with oxide it cannot conduct the flame-rectification signal, so the control shuts off the gas as a safety response. Cleaning the sensor typically restores operation. This is a very common no-heat service call.

When measuring the actual airflow of an installed system, which measurement helps diagnose a restrictive duct system?

• a.Refrigerant subcooling at the liquid line
• b.Gas manifold pressure at the valve outlet
• c.Total external static pressure at the air handler✓
• d.Condenser saturation temperature at the coil

Measuring total external static pressure and comparing it to the blower's rating reveals whether ductwork, filters, or coils are too restrictive. High static pressure indicates undersized or dirty components limiting airflow. It is a key airflow diagnostic tool.

A capacitor that reads well below its rated microfarad value should be treated how?

• a.Left in service
• b.Replaced with one of the correct rating✓
• c.Charged with refrigerant
• d.Bypassed with a jumper

A capacitor measuring significantly below its labeled microfarad rating is weak and cannot deliver the needed phase shift, causing hard starting, overheating, and high amp draw. It should be replaced with a capacitor of the same voltage and microfarad rating. Never bypass a required capacitor.

Recommended routine maintenance to preserve airflow and efficiency includes what?

• a.Adding refrigerant at every service visit
• b.Replacing the compressor once a year
• c.Changing filters and cleaning the coils✓
• d.Removing the condensate trap each spring

Routine maintenance such as changing filters, cleaning evaporator and condenser coils, and clearing condensate drains preserves airflow, capacity, and efficiency. Adding refrigerant should only follow a diagnosed leak and proper charging. Regular service prevents many common failures.

A technician measuring compressor amp draw far above the rated load amps (RLA) should suspect what?

• a.A healthy compressor under normal load
• b.High head pressure or failing windings✓
• c.An oversized air filter at the return
• d.Low control voltage at the thermostat

Amp draw well above the nameplate RLA indicates the compressor is overloaded, which can stem from high head pressure, low voltage, or degrading windings. Continued operation risks overheating and failure. The technician investigates head pressure, voltage, and mechanical condition.

The most likely cause of no cooling when the thermostat calls but the outdoor unit is completely silent is what?

• a.Low refrigerant subcooling at the condenser coil
• b.A dirty air filter at the return grille
• c.Lost power, failed contactor, or open safety✓
• d.Excess superheat in the suction line

A silent outdoor unit on a cooling call usually points to an electrical issue: tripped breaker, blown fuse, failed contactor, or an open safety such as a float switch or high-pressure switch. The technician traces control voltage and power to isolate the fault. Refrigerant issues usually still allow the unit to run.

An ECM (electronically commutated motor) blower offers what advantage over a standard PSC motor?

• a.It operates without any electricity
• b.Variable speed and better energy efficiency✓
• c.It eliminates the need for ductwork
• d.It removes refrigerant from the charge

ECM blower motors can vary speed to maintain target airflow across changing static pressure and generally use less energy than fixed-speed PSC motors. This improves comfort and efficiency and supports California energy goals. They are diagnosed differently, often through control signals and modules.

When a heat pump is stuck in cooling on a heat call, which component is a prime suspect?

• a.The condensate trap at the air handler
• b.The return air filter at the grille
• c.The reversing valve or its solenoid coil✓
• d.The supply registers in the rooms

If a heat pump blows cold air on a heating call, the reversing valve may be stuck or its solenoid coil or control signal may have failed, leaving the system in cooling mode. The technician checks the coil, the control voltage, and valve operation. A stuck valve often requires replacement.

Under Cal/OSHA, what is the purpose of a lockout/tagout (LOTO) procedure?

• a.To label refrigerant recovery cylinders
• b.To secure energy sources during service✓
• c.To measure superheat at the suction line
• d.To size the supply and return ductwork

Lockout/tagout requires de-energizing and physically locking energy-isolating devices, then tagging them, so machinery cannot be energized while a technician services it. This protects workers from electrical shock and unexpected startup. Cal/OSHA Title 8 sets the specific requirements.Cal/OSHA Title 8

Carbon monoxide is dangerous primarily because it is what?

• a.A visible green gas that has a sharp, acrid odor
• b.A refrigerant used in older sealed systems
• c.A colorless, odorless byproduct of combustion✓
• d.A vapor much heavier than refrigerant vapor

Carbon monoxide is a colorless, odorless gas produced by incomplete combustion of fuels, and it can be deadly because occupants cannot detect it. Cracked heat exchangers, poor venting, or inadequate combustion air can produce it. CO detectors and proper venting are essential safeguards.

A cracked heat exchanger in a gas furnace is a serious hazard because it can do what?

• a.Increase the cooling capacity of the indoor coil
• b.Let combustion gases mix with the supply air✓
• c.Lower the refrigerant charge in the system
• d.Improve airflow through the heat exchanger

A cracked heat exchanger can let flue gases, including carbon monoxide, leak into the circulating supply air and be distributed through the home. This is a life-safety hazard requiring the furnace to be shut down until repaired or replaced. Inspection for cracks is a standard safety check.

Cal/OSHA defines a confined space as one that has what characteristics?

• a.Any outdoor area with restricted equipment access
• b.Any interior room fitted with a door
• c.Limited entry, not for continuous occupancy✓
• d.Only spaces located below ground level

A confined space is large enough to bodily enter and perform work, has limited or restricted entry and exit, and is not designed for continuous occupancy, such as certain tanks, vaults, or attics. Permit-required confined spaces have added atmospheric or engulfment hazards. Cal/OSHA sets entry procedures and monitoring requirements.Cal/OSHA Title 8

When using a portable ladder, a safe practice is to maintain what?

• a.One hand on a tool at all times
• b.Three points of contact and proper ladder angle✓
• c.The ladder on a slippery surface
• d.The top rung as a step

Maintaining three points of contact and setting a straight ladder at roughly a 4-to-1 angle greatly reduces fall risk. Ladders must be on stable, level surfaces and inspected before use. Cal/OSHA specifies ladder safety requirements to prevent falls, a leading cause of injury.Cal/OSHA Title 8

Refrigerant can cause frostbite because liquid refrigerant does what when it contacts skin?

• a.Warms the skin as it evaporates slowly
• b.Acts as a mild lotion on the skin
• c.Evaporates fast and freezes the tissue✓
• d.Has no effect on unprotected skin

Liquid refrigerant boils at very low temperatures at atmospheric pressure, so contact with skin or eyes rapidly absorbs heat and can cause frostbite. Technicians wear gloves and eye protection when handling refrigerant. Cylinders and lines must be handled carefully to avoid sudden releases.

Refrigerant cylinders should be stored and handled how?

• a.In direct sunlight above their rated temperature
• b.Secured upright, away from heat, and never overfilled✓
• c.Laid on their side near a flame
• d.Vented periodically to relieve pressure

Refrigerant cylinders must be kept below their rated temperature, secured to prevent falling, and never overfilled, because heat raises internal pressure dangerously. Overheating or overfilling can cause a cylinder to rupture. Proper storage and handling are basic refrigerant safety practices.

The California Mechanical Code (CMC) primarily governs what?

• a.Electrical wiring and circuit overcurrent protection
• b.Plumbing fixtures and drainage piping systems
• c.Heating, ventilating, and refrigeration systems✓
• d.Structural framing, foundations, and roofs

The CMC sets the rules for installing mechanical systems including furnaces, air conditioners, ventilation, and refrigeration, covering venting, combustion air, clearances, and equipment access. Electrical work falls under the CEC and plumbing under the CPC. Contractors coordinate across these codes.2022 California Mechanical Code (CMC)

The California Electrical Code (CEC) is the governing code for what portion of HVAC work?

• a.Gas venting and flue termination clearances
• b.Wiring, disconnects, and circuit protection✓
• c.Condensate drainage and trap design
• d.Combustion air openings and sizing

The CEC governs the electrical aspects of HVAC installations, including circuit sizing, disconnecting means, grounding, and overcurrent protection. Proper electrical work protects against shock and fire. HVAC technicians must follow the CEC for all power and control wiring.

Under the California Plumbing Code, condensate waste from HVAC equipment is generally treated as what?

• a.Potable water that is suitable for reuse
• b.Fuel gas piping under pressure
• c.Drainage discharged to an approved point✓
• d.Combustion air for the appliance

HVAC condensate is drainage governed by the California Plumbing Code and must terminate at an approved point, not create a nuisance or hazard. Improper discharge onto walkways or into unapproved locations is a violation. Proper drainage prevents damage and slip hazards.2022 California Mechanical Code (CMC)

Personal protective equipment (PPE) commonly required when brazing refrigerant lines includes what?

• a.A disposable dust mask worn alone
• b.Eye protection, gloves, and ventilation✓
• c.No protection is required for short jobs
• d.Hearing protection and a hard hat only

Brazing produces intense heat, bright light, and potentially harmful fumes, so eye protection, gloves, and adequate ventilation are needed. Nitrogen purging reduces harmful phosgene-type byproducts from certain fluxes and coatings. Cal/OSHA requires appropriate PPE for the hazards present.Cal/OSHA Title 8

Why is a carbon monoxide alarm recommended or required in dwellings with fuel-burning appliances?

• a.To detect refrigerant leaks inside the home
• b.To measure indoor humidity levels
• c.To warn occupants of dangerous CO levels✓
• d.To sense high refrigerant head pressure

CO alarms detect rising carbon monoxide and warn occupants because the gas is otherwise undetectable by human senses. California law requires CO alarms in most dwellings with fuel-burning appliances or attached garages. They are a critical last line of defense against CO poisoning.

Before working inside an energized electrical panel is unavoidable, a technician should do what to reduce shock risk?

• a.Wear cotton work gloves and a long shirt
• b.Use insulated tools and appropriate PPE✓
• c.Wet the work area to reduce dust
• d.Remove all panel covers permanently

When de-energizing is not feasible, Cal/OSHA safe work practices call for insulated tools, appropriate PPE, and careful technique to reduce shock and arc-flash risk. Whenever possible, the circuit should be de-energized and locked out first. Working live is a last resort with added precautions.Cal/OSHA Title 8

Adequate ventilation air in occupied buildings is important because it does what?

• a.It raises the refrigerant charge in the system
• b.It reduces static pressure in the ducts
• c.It dilutes indoor contaminants with fresh air✓
• d.It lowers the equipment's SEER rating

Ventilation introduces outdoor air to dilute odors, carbon dioxide, and other indoor contaminants, maintaining acceptable indoor air quality. The CMC and related standards set minimum ventilation rates for occupancies. Balancing ventilation with energy use is part of good system design.2022 California Mechanical Code (CMC)

A furnace's high-limit (temperature limit) switch protects the equipment by doing what?

• a.Metering gas continuously
• b.Shutting off the burners if the furnace overheats✓
• c.Increasing blower speed permanently
• d.Recovering refrigerant

The high-limit switch senses excessive heat exchanger temperature, typically from low airflow, and shuts off the burners to prevent overheating and fire. Repeated tripping signals an airflow problem such as a dirty filter or failing blower. It is a key safety control that must never be bypassed.

When entering a permit-required confined space, atmospheric testing should be performed to check for what?

• a.The color of the refrigerant vapor
• b.The dimensions of the ductwork inside the space
• c.Oxygen level and toxic or flammable gases✓
• d.The blower speed at the air handler

Before and during entry into a permit-required confined space, the atmosphere is tested for adequate oxygen and for toxic or flammable gases to ensure it is safe. Continuous monitoring and ventilation may be required. Cal/OSHA mandates these procedures to prevent asphyxiation and explosion.Cal/OSHA Title 8

A high-pressure safety switch on refrigeration equipment protects the system by doing what?

• a.Adding refrigerant when the pressure drops
• b.Stopping the compressor on high pressure✓
• c.Draining condensate from the coil pan
• d.Boosting the condenser fan speed

A high-pressure switch opens the control circuit and stops the compressor when head pressure rises to an unsafe level, such as from a failed condenser fan or blocked airflow. This prevents component rupture and damage. It should be diagnosed and reset only after the underlying cause is corrected.

Which practice best reduces the risk of heat illness for HVAC technicians working on hot rooftops?

• a.Skipping water breaks in order to finish faster
• b.Wearing heavy dark clothing at midday
• c.Providing water, rest, shade, and pacing✓
• d.Avoiding all fluids while on the roof

Cal/OSHA heat illness prevention calls for access to water, shade, and rest breaks, plus acclimatization and pacing during high temperatures. Rooftop HVAC work exposes technicians to extreme heat, raising the risk of heat exhaustion or stroke. Recognizing symptoms early and hydrating are essential.Cal/OSHA Title 8

You are running a Manual J load for a house in Sacramento. Which outdoor temperatures belong in the calculation?

• a.The published 1% summer and 99% winter design temperatures for that location✓
• b.The record high and record low ever measured at the airport
• c.The average high and average low for July and January
• d.The temperatures forecast for the week the system is commissioned

Manual J sizes to the 1% cooling and 99% heating design conditions, so the system meets load in nearly all hours without being sized for rare extremes. Record highs and lows occur a few hours a decade and would grossly oversize the equipment. Monthly averages sit far below the design condition and would undersize it. A weekly forecast has nothing to do with a load that must serve the house for twenty years.

A homeowner asks why you will not size the new condenser by the '400 square feet per ton' rule the last contractor used. What is the strongest technical answer?

• a.The rule ignores insulation, glazing, orientation, and infiltration, which drive the load✓
• b.Square-footage rules always undersize equipment in hot climates
• c.Square-footage rules are only valid for single-story houses
• d.The rule was written for evaporative coolers rather than refrigerated air

A per-square-foot rule assumes one construction type and one climate, while the actual load is set by envelope insulation, window area and orientation, shading, and air leakage. It is not a story-count problem, since a well-built two-story house can also be load-calculated. It does not always undersize; on a tight modern house it usually oversizes badly. And the rule is a general HVAC shortcut, not an evaporative-cooler convention.

A coil removes 30,000 BTU/hr total and 22,500 BTU/hr sensible. What is the sensible heat ratio?

• a.1.33
• b.0.25
• c.0.75✓
• d.0.60

Sensible heat ratio is sensible capacity divided by total capacity: 22,500 / 30,000 = 0.75. The 0.60 answer comes from misreading which number is total. The 1.33 figure is the ratio inverted, which can never exceed 1.0 for a cooling coil. And 0.25 is the latent fraction, the remainder of the total, not the sensible ratio.

Which house would you expect to have the highest latent portion of its cooling load?

• a.A tight new house with triple-glazed west-facing windows
• b.A leaky older house in a high desert climate with low occupancy and no cooking
• c.A tight new house in a dry inland valley with low occupancy
• d.A leaky older coastal house with high occupancy and frequent cooking✓

Latent load comes from moisture, and the leaky coastal house pulls in humid outdoor air while people and cooking add water vapor indoors. A tight, dry-climate house with few occupants has almost no moisture source. Large west glazing raises the sensible solar load, not the latent load. A leaky high-desert house admits plenty of air, but that air is very dry, so the latent gain stays small.

You calculate 1,800 CFM of supply air cooled from 78 F to 57 F. What sensible capacity does that represent?

• a.20,412 BTU/hr
• b.32,400 BTU/hr
• c.40,824 BTU/hr✓
• d.58,320 BTU/hr

Sensible BTU/hr = 1.08 x CFM x delta-T = 1.08 x 1,800 x 21 = 40,824. The 20,412 figure uses half the airflow. The 32,400 figure drops the 1.08 constant and multiplies CFM by delta-T alone in a different form. The 58,320 figure uses the 4.5 total-heat constant with a dry-bulb difference, which mixes an enthalpy formula with a temperature reading.

Manual S is being applied after the Manual J is finished. Which capacity must be compared to the calculated sensible load?

• a.The nominal tonnage printed on the condenser nameplate
• b.The gross capacity before blower motor heat is subtracted
• c.The sensible capacity of the matched coil and condenser at design conditions✓
• d.The total capacity listed in the AHRI directory at standard rating conditions

Manual S compares the equipment's expanded-performance sensible capacity at the actual design outdoor temperature, indoor wet bulb, and airflow against the Manual J sensible load. Nominal tonnage is a marketing rounding and can differ from real output by thousands of BTU. AHRI rating conditions of 95 F outdoors and 80/67 indoors rarely match the job's design conditions. And gross capacity overstates delivery because blower heat is a real penalty on a fan-coil system.

A duct system has 0.50 in. w.c. of external static available and a total effective length of 250 feet. What friction rate should be used for sizing?

• a.0.05 in. w.c. per 100 feet
• b.0.10 in. w.c. per 100 feet
• c.0.15 in. w.c. per 100 feet
• d.0.20 in. w.c. per 100 feet✓

Friction rate = available static x 100 / total effective length = 0.50 x 100 / 250 = 0.20 in. w.c. per 100 feet. The 0.10 answer is the common default friction rate, not the one this system computes. The 0.05 and 0.15 answers come from using the wrong effective length or dividing the static pressure by the wrong factor. Sizing at too low a friction rate would make the ducts needlessly large for the fan actually installed.

In Manual D, what is 'total effective length' of a duct run?

• a.The measured length plus the equivalent lengths of all fittings in the run✓
• b.The sum of the supply and return trunk lengths on the whole system
• c.The straight length multiplied by a fixed correction factor for flex duct
• d.The measured straight run of the longest supply trunk from the plenum to the boot

Total effective length adds equivalent length credits for elbows, takeoffs, boots, and terminals to the measured straight length, because fittings cause most of the pressure loss. Measuring only the straight trunk ignores fittings entirely and yields an optimistic friction rate. Adding every trunk on the system double-counts branches that are not in the same path. And a single blanket multiplier for flex cannot represent the specific fittings a given run contains.

A round duct must carry 600 CFM at about 800 feet per minute. What cross-sectional area does that require?

• a.0.50 square feet
• b.0.60 square feet
• c.0.75 square feet✓
• d.1.33 square feet

Area = CFM / velocity = 600 / 800 = 0.75 square feet. The 0.50 and 0.60 figures come from using 1,200 or 1,000 FPM instead of the stated velocity. The 1.33 figure is the calculation inverted, dividing velocity by CFM, which produces a number with no physical meaning here. Once area is known, the duct diameter follows from the area of a circle.

A homeowner complains of noisy registers on a system you did not install. Which design decision most likely caused it?

• a.The branch ducts were sized for a high velocity to save material✓
• b.The supply trunk was insulated to a higher R-value than required
• c.The return grille was installed in a hallway instead of a bedroom
• d.The equipment was sized from a room-by-room load rather than a block load

Noise at the register tracks air velocity, and undersized branches force the same CFM through less area, raising velocity and turbulence. Extra insulation on the trunk changes heat loss, not the sound at a register. A room-by-room load is the more accurate approach and would not create noise. Return location affects room-to-room pressure balance and comfort, but the whistling is generated at the undersized supply.

How does duct located in a vented attic affect a Manual J cooling load?

• a.It reduces the load because attic air pre-cools the supply
• b.It affects only the heating load, not the cooling load
• c.It has no effect on the load, because the ducts are inside the building footprint
• d.It adds conduction gain and leakage loss that must be included in the load✓

Ducts in an unconditioned attic gain heat through the insulation and lose conditioned air through leaks, and Manual J includes both as duct load. Being under the roofline is not the same as being inside the thermal envelope. Attic air in summer is far hotter than supply air, so it heats rather than pre-cools. And the penalty applies in both seasons, since the attic is also cold on a winter design morning.

A contractor replaces a furnace and more than 40 feet of duct in an existing California home. What compliance step is most likely triggered?

• a.Replacement of every register and grille in the house
• b.Recalculation of the electrical service load by an engineer
• c.Duct leakage testing verified by a third-party HERS rater✓
• d.A full Manual J submitted to the utility for rebate approval

California's energy standards require diagnostic duct leakage testing with independent HERS verification when a substantial portion of a duct system is replaced or the air handler is changed. A load calculation is good practice and often required for permitting, but it is not the third-party measure the alteration triggers. Registers are not required to be swapped as a condition of duct alteration. And service load recalculation belongs to electrical work, not duct alteration.California Energy Code (Title 24, Part 6)

A furnace is rated 80,000 BTU/hr input at 80% AFUE. What output should be compared to the calculated heat loss?

• a.100,000 BTU/hr
• b.80,000 BTU/hr
• c.72,000 BTU/hr
• d.64,000 BTU/hr✓

Output equals input times efficiency: 80,000 x 0.80 = 64,000 BTU/hr, and that is what actually reaches the house. Using 80,000 treats the fuel burned as if all of it were delivered, ignoring flue losses. The 72,000 figure applies 90% efficiency, which is a condensing furnace rating, not this one. The 100,000 figure divides by the efficiency, which sizes the appliance the wrong direction.

Which change to a house would reduce the design heating load the most on a cold winter night?

• a.Air sealing the attic plane and adding insulation over the ceiling✓
• b.Replacing north-facing windows with larger units of the same U-factor
• c.Painting the roof a lighter color to raise its solar reflectance
• d.Adding an exterior shade awning over the south-facing patio door

Heating load is driven by conduction and infiltration, so sealing leaks and insulating the ceiling attacks the two largest winter losses directly. Larger windows of the same U-factor increase area and therefore increase the loss. Awnings block summer sun and can even raise the winter load by blocking useful solar gain. A cool roof lowers summer attic temperature but does almost nothing on a night with no sun.

What does the balance point of an air-source heat pump represent?

• a.The outdoor temperature at which COP falls to 1.0
• b.The outdoor air temperature at which the defrost cycle first begins to initiate
• c.The outdoor temperature at which heat pump capacity equals the building load✓
• d.The indoor setpoint at which the auxiliary heat is locked out

The balance point is where the falling heat pump output line crosses the rising building heat loss line; below it, supplemental heat is needed. Defrost initiation depends on coil temperature and humidity, not on this crossing. Auxiliary lockout is a control setting the installer chooses and is not the definition. And a COP of 1.0 is the point where the heat pump is no better than resistance heat, which is a different and much colder condition.

A 3-ton system moves 1,200 CFM. The blower is slowed to 900 CFM to improve dehumidification. What is the expected effect?

• a.Both sensible and latent capacity rise together
• b.Total capacity is unchanged because the compressor is unchanged
• c.Sensible capacity rises and latent capacity drops
• d.Sensible capacity drops and latent capacity rises✓

Less air over the coil makes the coil colder, so more moisture condenses while the sensible transfer falls. Both cannot rise, because the split between sensible and latent shifts rather than growing. Raising airflow, not lowering it, is what increases sensible and reduces latent. And total capacity does change, since coil performance depends on air mass flow and coil temperature, not on the compressor alone.

The latent heat formula for airflow in CFM and moisture difference in grains per pound uses which constant?

• a.0.24
• b.1.08
• c.4.5
• d.0.68✓

Latent BTU/hr = 0.68 x CFM x grains difference, where the constant folds in air density and the latent heat of water vapor. The 1.08 constant belongs to the sensible formula with a dry-bulb difference. The 4.5 constant is used with enthalpy in BTU per pound to get total heat. And 0.24 is the specific heat of air in BTU per pound per degree F, an input to those constants rather than the constant itself.

You measure 1,000 CFM entering a coil at 30 BTU/lb enthalpy and leaving at 22 BTU/lb. What total capacity is the coil delivering?

• a.8,640 BTU/hr
• b.27,000 BTU/hr
• c.36,000 BTU/hr✓
• d.52,000 BTU/hr

Total heat = 4.5 x CFM x enthalpy difference = 4.5 x 1,000 x 8 = 36,000 BTU/hr. The 8,640 figure uses the 1.08 sensible constant with the enthalpy difference, which mixes formulas. The 27,000 figure uses a 6 BTU/lb difference rather than the 8 given. The 52,000 figure would require a much larger enthalpy drop than the readings show.

Why is a room-by-room Manual J load required before a duct design, even when a block load is available?

• a.Because each branch duct must be sized to the CFM its own room needs✓
• b.Because block loads systematically understate whole-house tonnage
• c.Because permit officials will not accept a block load for equipment sizing
• d.Because latent load can only be calculated on a room-by-room basis

Manual D distributes air in proportion to each room's load, so branch sizing depends on room-level numbers that a block load never produces. A block load gives an accurate whole-house total; it simply does not break it down. Jurisdictions commonly accept a block load for equipment selection alone. And latent load is calculated at the block level routinely, so that is not the reason.

A bedroom has a calculated cooling load of 3,000 BTU/hr in a house whose total cooling load is 24,000 BTU/hr and whose blower moves 1,200 CFM. What supply airflow should the room receive?

• a.100 CFM
• b.120 CFM
• c.135 CFM
• d.150 CFM✓

The room holds 3,000 / 24,000 = 12.5% of the load, so it gets 12.5% of 1,200 CFM, or 150 CFM. The 100 and 120 figures come from using a lower total airflow or rounding the load fraction down. The 135 figure splits the difference without following the proportion. Proportional distribution is what keeps room temperatures even across the house.

Two identical houses sit side by side, one with its main glazing facing west and one facing north. How do their cooling loads compare?

• a.The west-facing house has a higher peak cooling load✓
• b.The north-facing house has a higher peak cooling load
• c.The difference appears only in the latent portion of the load
• d.The loads are identical because the glazing area is the same

West glass takes direct low-angle sun during the hottest hours, producing the largest solar gain and setting the afternoon peak. North glass in California receives mostly diffuse light, so its gain is far smaller. Equal area does not mean equal gain, because orientation controls how much solar radiation strikes the glass. And solar gain is sensible heat; it does not change the moisture in the space.

Which glazing property most directly governs the solar portion of a window's cooling load?

• a.The solar heat gain coefficient of the window✓
• b.The U-factor of the window assembly
• c.The visible transmittance of the glass
• d.The air leakage rating of the operable window sash

The solar heat gain coefficient is the fraction of incident solar energy that ends up as heat in the room, so it scales the solar gain term directly. U-factor governs conduction driven by the indoor-outdoor temperature difference, which is a separate term. Visible transmittance describes daylight, and a glass can pass light while blocking heat. Air leakage feeds the infiltration term, not the solar term.

A wall measures 400 square feet with a U-factor of 0.075 and a design temperature difference of 40 F. What is its heat loss?

• a.600 BTU/hr
• b.1,200 BTU/hr✓
• c.2,400 BTU/hr
• d.16,000 BTU/hr

Heat loss = U x Area x delta-T = 0.075 x 400 x 40 = 1,200 BTU/hr, and every opaque assembly in the house is totaled the same way. The 600 figure uses half the temperature difference. The 2,400 figure doubles either the area or the delta-T. The 16,000 figure treats 0.075 as an R-value and divides by it, which inverts the relationship between thermal resistance and conductance.

A wall assembly has a total R-value of 20. What is its U-factor?

• a.0.20
• b.0.10
• c.0.08
• d.0.05✓

U-factor is the reciprocal of R-value, so 1 divided by 20 gives 0.05, and that number is what the heat loss formula multiplies by area and temperature difference. The 0.20 answer simply moves the decimal point on the R-value. The 0.10 answer is the reciprocal of R-10, a much poorer wall. The 0.08 answer corresponds to roughly R-12.5, which is also lower performance than the assembly described.

Which internal gain is normally the largest single line item in a residential Manual J for an occupied kitchen and living area?

• a.Appliances and lighting operating during the peak hour✓
• b.The blower motor heat added by the furnace fan
• c.The sensible heat given off by occupants who are sleeping
• d.Heat conducted through interior partition walls

Cooking appliances and lighting release substantial sensible heat in the same afternoon hour when the envelope load peaks, so they dominate internal gains. Sleeping occupants give off the lowest metabolic heat of any activity level and are counted at a reduced rate. Interior partitions separate two conditioned rooms at nearly the same temperature, so conduction across them is close to zero. Blower heat is real but is handled as an equipment correction, not a room internal gain.

A 90,000 BTU/hr input furnace must hold a 50 F temperature rise. Roughly what airflow is required at 80% efficiency?

• a.About 900 CFM
• b.About 1,330 CFM✓
• c.About 1,670 CFM
• d.About 2,000 CFM

Output is 90,000 x 0.80 = 72,000 BTU/hr, and CFM = 72,000 / (1.08 x 50) = about 1,330. The 900 figure would give a rise near 74 F and would trip the limit switch. The 1,670 and 2,000 figures use the full input rather than the output, which overstates the air the furnace actually needs and would push the rise below the rating plate range.

Where does a technician find the acceptable temperature rise range for a specific gas furnace?

• a.In the ACCA Manual J tables for the climate zone
• b.In the California Energy Code residential compliance forms
• c.On the equipment rating plate or in the installation instructions✓
• d.In the AHRI certified ratings directory listing for that model number

Temperature rise is a manufacturer-specified range printed on the rating plate and repeated in the installation manual, and the blower must be set to land inside it. Manual J produces building loads, not appliance operating limits. Title 24 compliance forms document energy features, not the rise band. And the AHRI directory reports efficiency and capacity ratings, not the allowable rise for a given model.

Fan laws describe blower behavior. If blower speed increases 25%, what happens to the power the motor must draw?

• a.It increases about 25%
• b.It stays the same because the motor is constant speed
• c.It increases about 56%
• d.It increases about 95%✓

Power varies with the cube of speed, so 1.25 cubed is about 1.95, roughly a 95% increase. Airflow, not power, varies directly with speed, which is where the 25% answer comes from. Static pressure varies with the square of speed, which gives the 56% figure. And a blower whose speed was just changed is by definition not running at constant speed.

A whole-house exhaust fan removes 100 CFM continuously from a tight new home. How should the load calculation treat that air?

• a.As a latent-only load with no sensible component
• b.As irrelevant because mechanical ventilation is outside Manual J
• c.As additional outdoor air that must be conditioned✓
• d.As a reduction in load because stale air is removed

Air exhausted from a house is replaced by outdoor air entering somewhere, and that air arrives at design temperature and humidity, so it becomes load. It cannot reduce the load, because the incoming replacement air is exactly what the equipment must condition. It carries both a temperature difference and a moisture difference, so restricting it to latent is wrong. And deliberate ventilation air is specifically accounted for in a modern load calculation.

A two-story house cools unevenly, with the upstairs several degrees warmer every afternoon. Which design remedy addresses the cause rather than the symptom?

• a.Lower the thermostat setpoint until the upstairs is comfortable
• b.Install a larger condenser to raise total system capacity
• c.Calculate loads floor by floor and redistribute airflow or zone the system✓
• d.Increase the refrigerant charge to lower the supply air temperature upstairs

Upstairs carries more roof and solar gain, so the fix is to match delivered CFM to each floor's actual load, by redistribution or by zoning. Dropping the setpoint overcools the downstairs while the upstairs still lags. Overcharging raises head pressure and can flood the compressor without moving more air upstairs. And a larger condenser adds capacity to a system that is already delivering it to the wrong floor.

What is the main design risk of using a bypass duct with a zoned residential system?

• a.It prevents the zone dampers from ever closing fully
• b.It makes the outdoor unit short cycle on high head pressure
• c.It raises static pressure so high that the blower stalls
• d.It recirculates cold air to the coil and can freeze it during small zone calls✓

A bypass sends already-cooled supply air back to the return, dropping entering air temperature until the coil ices when only one small zone calls. It actually relieves static pressure rather than raising it, which is why it is installed in the first place. It has no mechanical effect on damper travel. And the low-side starvation it creates tends to lower head pressure, not raise it into a high-pressure trip.

Return air paths are being designed for bedrooms that have no dedicated return grille. What is the design objective?

• a.Keep the bedroom at a measurable negative pressure while occupied
• b.Ensure each bedroom receives more return CFM than supply CFM
• c.Limit the pressure the closed door creates between the room and the hall✓
• d.Route the transfer air path through the attic to gain extra effective length

Transfer grilles, jump ducts, or undercuts exist to keep room pressurization small when the door closes so supply air can actually enter. Deliberately returning more than is supplied would depressurize the room and pull in attic or garage air. A measurable negative pressure is the defect being avoided, not the goal. And running the path through an unconditioned attic adds heat gain and leakage to a transfer that should stay inside the envelope.

You measure total external static pressure of 1.1 in. w.c. on a system whose blower is rated for 0.5 in. w.c. What is the first consequence for the design?

• a.The compressor will draw amperage above its rated load amps
• b.The condensate trap will siphon dry on every cycle
• c.The furnace will fail to ignite on a call for heat
• d.Airflow will fall below the design CFM, cutting capacity✓

A blower operating far beyond its rated external static moves much less air than its table value, so delivered capacity and temperature split both suffer. Compressor amperage is set by refrigerant load and voltage, and low airflow typically lowers it rather than raising it above RLA. Ignition depends on the gas train and flame proving, not on duct static. And trap siphoning is caused by blower suction at the drain, a separate and much smaller pressure issue.

Which pair of measurements is used to determine total external static pressure on a residential air handler?

• a.Velocity pressure at the register and velocity pressure at the grille
• b.Supply plenum pressure and outdoor barometric pressure
• c.Filter pressure drop and coil pressure drop added together
• d.Supply plenum pressure and return pressure at the equipment✓

Total external static is the pressure the blower works against outside the cabinet, read as supply-side positive plus return-side negative at the equipment. Barometric pressure is an ambient reading and is not part of a duct measurement. Filter and coil drops are internal component losses that many manufacturers exclude from external static. And velocity pressure measures air speed, which is not the static resistance the fan table uses.

A designer wants to reduce the friction loss in a long branch run without changing the duct diameter. What is the most effective option?

• a.Wrap the duct with a higher R-value insulation blanket
• b.Replace sharp fittings with long-radius elbows and smooth boots✓
• c.Add a manual balancing damper near the takeoff
• d.Increase the blower speed to push more air through the branch duct

Fittings contribute most of the effective length in a branch, so long-radius elbows and better boots cut pressure loss substantially without resizing. Insulation changes heat transfer, not friction. A balancing damper deliberately adds resistance to reduce flow, which is the opposite of the goal. And more blower speed does not lower friction; it raises pressure loss further while burning more fan power.

Flexible duct is installed with visible sag and slack between supports. How does this affect the Manual D design?

• a.Effective friction rises well above the tables, so delivered CFM drops✓
• b.It matters only on return ducts, since supply ducts are pressurized anyway
• c.Capacity improves because the longer path increases heat exchange
• d.Only noise increases, because friction depends on diameter alone

Manual D friction values for flex assume the duct is pulled taut, and sagging inner liner adds turbulence that can cut delivered airflow sharply. Friction depends on interior surface condition and path shape, not diameter alone. Extra path length in an unconditioned space adds losses rather than useful heat exchange. And the friction penalty applies equally to return ducts, which are just as sensitive to added resistance.

Which measurement pair lets a technician determine the latent capacity a coil is actually producing?

• a.Suction pressure and suction line temperature
• b.Entering and leaving wet-bulb temperature✓
• c.Supply plenum static and return plenum static
• d.Entering and leaving dry-bulb temperature

Wet-bulb readings translate to enthalpy, and the drop in enthalpy beyond the sensible portion is the latent work the coil is doing. Dry-bulb alone captures only sensible heat and says nothing about moisture removed. Suction pressure and line temperature give superheat, a refrigerant-side charge check. And static pressures describe duct resistance, not the moisture content of the air.

A house has a design cooling load of 22,000 BTU/hr. Available equipment comes in 1.5, 2, 2.5, and 3 ton sizes. Which selection best follows Manual S?

• a.1.5 ton, because smaller equipment runs longer and dehumidifies much better
• b.2 ton, verified against the expanded performance data at design conditions✓
• c.2.5 ton, to leave headroom for hotter than design summers
• d.3 ton, because the next size up protects against future additions

A 2-ton unit sits closest to the 22,000 BTU/hr load, and Manual S then confirms its sensible and latent split at the actual design conditions. A 1.5-ton unit is roughly 4,000 BTU short and will not hold setpoint on a design day. A 2.5-ton unit exceeds the Manual S oversizing allowance and short cycles. And sizing for a hypothetical future addition penalizes comfort and efficiency for every year until that addition exists.

Two houses have the same floor area, but one has 12 air changes per hour at 50 pascals and the other has 3. What does that tell you about their loads?

• a.The loads are equal because area drives infiltration
• b.The tighter house has the higher heating load
• c.The difference shows up only in the summer cooling load
• d.The leakier house has the higher infiltration load in both seasons✓

A blower-door result of 12 ACH50 means far more air exchange than 3 ACH50, and that unconditioned air is load in both winter and summer. Tightness reduces load, so the tighter house cannot be the higher one. Floor area is only one input; leakage area is what drives infiltration. And infiltration is driven by temperature and wind differences year round, not summer only.

Why does Manual J use a cooling load temperature difference rather than the plain indoor-outdoor difference for roofs and walls?

• a.To convert the BTU per hour result into tons of refrigeration directly
• b.To correct the calculation for elevation above sea level
• c.To include the latent gain absorbed by the roof sheathing
• d.To account for solar absorption and the mass delay of the assembly✓

Sunlit opaque surfaces run hotter than the air and release that heat on a lag governed by mass, so an adjusted temperature difference represents the real driving force. Converting to tons is a simple division at the end and needs no such adjustment. Elevation corrections apply to air density in the airflow constants, not to wall conduction. And roof sheathing does not add moisture to the space, so no latent term is involved.

Design airflow for a heat pump in heating mode is generally set how, relative to cooling?

• a.At or near cooling airflow, because the same coil must reject heat indoors✓
• b.Independently, since the same blower cannot serve both modes
• c.Well below cooling airflow to raise supply air temperature
• d.At exactly half of cooling airflow to protect the compressor

A heat pump uses the indoor coil as a condenser, and it needs comparable air mass flow to keep head pressure and capacity in range, so heating airflow is set at or near the cooling value. Cutting airflow to raise supply temperature drives head pressure up and can trip the high-pressure control. Halving the airflow is a furnace-style adjustment that does not protect a heat pump compressor. And one variable-speed or multi-tap blower routinely serves both modes.

Which situation makes an oversized air conditioner most likely to leave a house clammy?

• a.A dry inland climate where the latent load is very small
• b.A well-shaded house with very low solar gain through glass
• c.A coastal climate where a large share of the load is latent✓
• d.A house with very high daytime internal sensible gain from appliances

Oversized equipment satisfies the thermostat on short cycles, and short run times remove little moisture, which is most obvious where the latent load is large. In a dry climate there is little moisture to remove, so the defect stays hidden. Low solar gain reduces sensible load but does not by itself create the clammy complaint. And a high sensible gain lengthens run times, which actually helps dehumidification.

A commercial space is designed for outdoor air ventilation. What two factors normally set the required outdoor air rate?

• a.Floor area and the design number of occupants✓
• b.Ceiling height and lighting power density
• c.Roof insulation R-value and window orientation
• d.Supply air temperature and the number of diffusers

Ventilation standards compute outdoor air as a rate per person plus a rate per unit of floor area, so occupancy and area drive the number. Ceiling height and lighting affect load and dilution volume but are not the rate basis. Supply temperature and diffuser count are distribution choices made after the rate is known. And envelope properties change the thermal load rather than the required fresh air.

A restaurant kitchen has a 3,000 CFM exhaust hood. What must the mechanical design provide?

• a.A return duct sized for 3,000 CFM back to the air handler
• b.A relief damper sized to exhaust an additional 3,000 CFM
• c.An outdoor air economizer locked open during cooking hours
• d.Makeup air roughly equal to the exhausted volume✓

Air removed by a hood must be replaced, or the building goes negative and pulls air backward through vents and doors. A return duct recirculates conditioned air and does not replace what left the building. A second relief path would make the negative pressure worse. And an economizer is a free-cooling control strategy, not a code-recognized substitute for engineered makeup air.

You are designing for a job site at 5,000 feet elevation. What correction does the airflow calculation need?

• a.Use the 4.5 constant in place of 1.08 for all sensible work
• b.No correction, because CFM is a volume measurement
• c.Multiply the required CFM by the ratio of sea-level pressure to local pressure
• d.Reduce the sensible constant because air is less dense at altitude✓

The 1.08 constant assumes sea-level air density, and thinner air carries less heat per cubic foot, so the constant must be reduced at altitude. Ignoring the correction overstates the capacity a given CFM can deliver. There is no single pressure-ratio multiplier applied to the CFM target itself. And 4.5 is the total-heat constant used with enthalpy, which does not substitute for the sensible constant.

A new duct system is being installed in a vented attic in California. Which requirement most directly affects the duct design?

• a.Flexible duct is prohibited anywhere outside conditioned space
• b.Ducts in unconditioned space must meet a minimum insulation R-value✓
• c.All duct joints must be soldered rather than mechanically fastened and taped
• d.Return ducts may not exceed forty feet of developed length

California's energy standards set a minimum duct insulation level for ducts outside conditioned space, which affects sizing because insulation thickness eats into the available cavity. Ducts are sealed with mastic or listed tape, not solder. There is no blanket forty-foot cap on return length. And listed flexible duct is permitted in attics when it is properly supported and insulated.California Energy Code (Title 24, Part 6)

Which approach best reduces duct load on a new California house at the design stage?

• a.Locating the ducts and air handler inside conditioned space✓
• b.Adding a bypass duct to relieve static pressure at low load
• c.Using rigid metal duct instead of insulated flexible duct
• d.Increasing the supply air temperature difference across the coil

Ducts inside the thermal envelope lose heat and leak air into the conditioned space, so both the conduction and leakage penalties nearly disappear. Changing the coil temperature split does not change what the ducts lose on the way to the register. A bypass increases mixing losses rather than reducing duct load. And material choice affects friction and durability, but a metal duct in a hot attic still conducts and leaks.

A homeowner wants a ductless mini-split for a 400 square foot converted garage. What determines the head capacity you select?

• a.The rated airflow of the indoor head at its highest fan speed
• b.The nominal capacity of the outdoor unit divided evenly by the number of heads
• c.A load calculation for that room including the uninsulated slab and door✓
• d.The maximum line set length the manufacturer permits for the model

The head must match the room's own calculated load, and a converted garage has envelope details, a large door, and slab conditions that a general rule would miss. Splitting the outdoor unit's rating evenly ignores what each room actually needs. Fan airflow describes distribution capability, not thermal capacity. And line set length is an installation limit that affects performance derating, not the capacity requirement.

What happens to a fixed-capacity air conditioner's total capacity as outdoor temperature rises from 85 F to 105 F?

• a.Capacity falls only if the indoor wet bulb also rises
• b.Capacity falls because condensing pressure and temperature rise✓
• c.Capacity rises because the compression ratio increases
• d.Capacity stays constant because the compressor displacement is fixed

Hotter outdoor air raises condensing temperature and head pressure, which reduces mass flow and refrigerating effect, so capacity drops just as the building load peaks. A higher compression ratio hurts volumetric efficiency rather than helping capacity. Fixed displacement does not mean fixed capacity, because the density of the vapor entering the cylinder changes. And the drop happens on the outdoor side regardless of what the indoor wet bulb does.

A designer must choose between a single-stage and a two-stage condenser for a house with a wide load swing. What is the main comfort argument for two-stage?

• a.It delivers more total cooling capacity from the same physical cabinet size
• b.It eliminates the need for a variable-speed indoor blower
• c.It removes the need for an accurate Manual J load calculation
• d.It runs longer at low capacity, improving humidity control and evenness✓

Two-stage equipment spends most hours at reduced output, producing long run times that even out temperatures and pull more moisture from the air. It does not increase peak capacity for the same cabinet size. Accurate load calculation matters more with staged equipment, not less, because the low stage must match the part-load condition. And a matched variable-speed blower is usually what makes the low stage work properly.

During design you find the return grille face velocity will be about 800 feet per minute. What is the likely outcome?

• a.Objectionable noise at the grille and elevated return static✓
• b.Improved mixing that reduces temperature stratification in the room
• c.Lower static pressure because the air moves through quickly
• d.Excellent filtration because dust is captured at high velocity

Return grilles are normally kept in the range of a few hundred feet per minute, and 800 FPM produces roar and a large pressure drop. High velocity does not improve filtration; it increases the pressure drop across the media and can drive dust deeper into it. Static pressure rises rather than falls when air is forced through a small free area. And mixing is a supply-side diffuser function, not a return-grille one.

Which room would you expect to need the highest CFM per square foot in a residential design?

• a.An interior hallway with no exterior walls or windows
• b.A west-facing sunroom with large single-pane glazing✓
• c.A carpeted den under a well-insulated attic
• d.A north-facing bedroom on the ground floor

Airflow is distributed in proportion to load, and a sunroom with large west glass carries by far the highest gain per square foot. An interior hallway has almost no envelope load at all. A north-facing ground-floor bedroom sees modest conduction and diffuse light. And a den under deep attic insulation has one of the lowest gains in the house.

A technician measures 20 F temperature split across an evaporator on a 78 F day with 50% indoor humidity. How should that be interpreted?

• a.As evidence of a restricted metering device
• b.As a normal split that still needs airflow and charge verified separately✓
• c.As proof the refrigerant charge is correct
• d.As a sign the system is significantly oversized for the house

A split near 20 F is within the usual range for those conditions, but split alone cannot separate an airflow problem from a charge problem, so superheat, subcooling, and CFM still must be checked. It is not proof of correct charge, since low airflow with low charge can produce a normal-looking split. A restricted metering device would usually show a much larger split with very low suction. And sizing is determined by run time and load calculation, not by split.

What does a psychrometric chart let a designer determine that a thermometer alone cannot?

• a.The friction rate needed to size a duct run
• b.The static pressure the blower must overcome
• c.The moisture content and enthalpy of the air at a given state✓
• d.The saturation temperature of the refrigerant at a given pressure

A psychrometric chart plots dry bulb against humidity and yields wet bulb, dew point, grains of moisture, and enthalpy, which is what the latent and total heat formulas need. Static pressure is a duct measurement read with a manometer. Refrigerant saturation comes from a pressure-temperature chart for the specific refrigerant. And friction rate is calculated from available static and effective length in Manual D.

Air enters a coil at 80 F dry bulb and 67 F wet bulb and leaves at 57 F dry bulb and 56 F wet bulb. What is happening to the air?

• a.It is being heated and humidified at the same time
• b.It is being dehumidified without any temperature change
• c.It is being cooled and dehumidified simultaneously✓
• d.It is being cooled without any moisture removal

Both dry bulb and wet bulb fall, and a falling wet bulb means enthalpy and moisture content have dropped, so the coil is doing sensible and latent work together. Sensible-only cooling would drop dry bulb while moisture content stayed put. Nothing here is being heated, since both readings decrease. And the dry bulb fell 23 degrees, so this is clearly not a constant-temperature process.

In a light commercial rooftop design, why is the return air path through a ceiling plenum a design concern?

• a.Materials exposed in the plenum must meet flame and smoke limits✓
• b.Plenum returns eliminate the need to calculate return static pressure
• c.Plenum returns always require a fire damper at every wall
• d.Plenum returns cannot be used with packaged rooftop equipment

When a ceiling cavity is used as a return plenum, wiring, insulation, and other materials in that space must be rated for flame spread and smoke development. Packaged rooftops are commonly applied with plenum returns. Fire dampers are required where the assembly penetrates a rated barrier, not at every wall. And return static pressure must still be measured and included in the fan's external static.

A load calculation shows a heating load of 48,000 BTU/hr and a cooling load of 18,000 BTU/hr in a mountain California climate zone. What equipment strategy fits best?

• a.Average the two loads and select one system to match the average
• b.Size both the furnace and the condenser to match the heating load for simplicity
• c.Size the furnace to the heating load and the condenser to the cooling load✓
• d.Size the condenser to the heating load and add electric strip heat

A split system has independent heating and cooling components, so each is selected against its own calculated load. Matching the condenser to the 48,000 BTU/hr heating number would put a 4-ton unit on an 18,000 BTU/hr cooling load and cause severe short cycling. Sizing on the heating load and adding strip heat compounds the same oversizing. And averaging two unrelated loads leaves both seasons mismatched.

You are asked to justify why the new system is smaller than the 5-ton unit being replaced. What is the most defensible explanation?

• a.Manufacturers now rate equipment at a lower outdoor temperature
• b.The original unit was sized by rule of thumb before the house was upgraded✓
• c.Smaller equipment is required by the state on every change-out
• d.Newer refrigerants deliver more capacity per nominal ton

Replacement loads routinely come in smaller because the original was guessed at, and windows, insulation, and air sealing have improved since. Refrigerant choice affects operating pressures and efficiency, not the tonnage a house needs. Rating conditions have not been moved to a lower outdoor temperature. And no state rule mandates downsizing; the load calculation is what justifies the selection.

A 100,000 BTU/hr furnace is being installed in a closet that draws combustion air from inside a tight house. What is the fundamental problem?

• a.The closet door must be louvered only on new construction
• b.Closet installations always require a listed vent damper
• c.Interior air is too dry to support a stable flame
• d.The interior volume may not supply enough air for complete combustion✓

Combustion air requirements are based on the volume of the space and the total input of the appliances, and a tight house cannot supply the needed volume without engineered openings to outdoors. Vent dampers are an efficiency device, not a combustion-air solution. Dry air burns fine; the issue is oxygen quantity, not humidity. And louvers or openings sized to the code method are required whenever the space is confined, in new and existing work alike.California Mechanical Code (Title 24, Part 4), Chapter 7

When the two-opening method is used to bring combustion air directly from outdoors, where must the openings be located?

• a.One within 12 inches of the top and one within 12 inches of the bottom✓
• b.One in the enclosure and one in an adjoining bedroom
• c.Both within 12 inches of the floor of the enclosure
• d.Both within 12 inches of the ceiling of the enclosure

The high opening admits or relieves warm air and the low opening supplies denser cool air, so the pair must straddle the enclosure top and bottom. Two high openings leave the lower part of the space without supply. Two low openings give no path for the buoyant air. And a bedroom is specifically not an acceptable source for appliance combustion air.California Mechanical Code (Title 24, Part 4), Chapter 7

You are replacing an 80% furnace with a condensing model on an existing Type B vent that also serves a natural-draft water heater. What must be evaluated?

• a.Whether the water heater alone can still vent safely in the oversized common vent✓
• b.Whether the water heater needs a larger gas supply line
• c.Whether the Type B vent can be reused for the condensing furnace flue
• d.Whether the vent must be relined with single-wall connector pipe

Removing the furnace from a common vent leaves an orphaned water heater in a vent sized for two appliances, which can fail to establish draft and spill flue gases. The Type B vent cannot serve the condensing furnace, whose acidic condensate requires listed plastic venting, so reuse is not the open question. Gas line sizing is unrelated to the venting change. And single-wall connector is not a lining material for a masonry or B-vent system.California Mechanical Code (Title 24, Part 4), Chapter 8

Why must a Category IV condensing furnace be vented with listed plastic pipe rather than Type B vent?

• a.Flue gases condense and the resulting condensate is corrosive✓
• b.Plastic pipe is lighter and easier to route through framing
• c.Type B vent cannot be routed horizontally through an exterior sidewall
• d.Plastic pipe resists the higher flue temperatures produced

A condensing appliance cools flue gas below its dew point, and the acidic liquid that forms would destroy metal vent. Ease of routing is a convenience, not the code reason. Type B vent can run horizontally within listed limits, so that is not the distinction. And the flue temperature of a condensing furnace is low, not high, which is exactly why it condenses.

A single-wall vent connector runs horizontally from a natural-draft furnace to the vertical vent. How should it be installed?

• a.With a downward trap at the appliance to catch soot
• b.Level, with no rise at all, to keep the run as short as possible
• c.Sloping downward toward the appliance to drain condensate
• d.Sloping upward toward the vent at least a quarter inch per foot✓

Buoyant flue gas needs continuous upward slope toward the vent so draft develops and gases do not stall in the connector. A level run offers no rise and invites spillage at the draft hood. Sloping toward the appliance sends flue gas and any moisture back into the equipment. And a trap in a vent connector would obstruct flow and create a condensate and soot pocket.California Mechanical Code (Title 24, Part 4), Chapter 8

A direct-vent sealed-combustion furnace is installed in a garage workshop. Why is this arrangement well suited to that space?

• a.It allows the return air to be taken from the garage itself
• b.It removes the requirement for a service disconnect
• c.It eliminates the need for a condensate drain
• d.It draws combustion air from outdoors, isolating it from garage vapors✓

A sealed-combustion appliance pipes its own air from outdoors, so the burner never breathes garage air that may carry gasoline or solvent vapors. It still condenses in most cases and still needs a drain. An electrical disconnect is required regardless of combustion type. And return air must never be taken from a garage, since that would draw contaminants into the living space.

A gas furnace is being set on the floor of an attached residential garage. Which installation requirement generally applies?

• a.The ignition source must be elevated unless the unit is listed for floor installation✓
• b.The furnace must be converted to propane before garage installation
• c.The furnace must be placed within 3 feet of the vehicle door
• d.The furnace must be enclosed in a fire-rated closet with a locked door

Gasoline vapors are heavier than air and pool near the slab, so appliances that generate a spark or flame are elevated above the floor unless they carry a listing that permits floor mounting. A locked rated closet is not the code remedy and would create service and combustion-air problems. Fuel conversion has nothing to do with vapor ignition risk. And placing the unit near the vehicle door increases physical impact exposure rather than reducing hazard.California Mechanical Code (Title 24, Part 4)

An appliance is installed in a garage where a vehicle can be driven near it. What additional protection is required?

• a.A dedicated smoke detector directly above the unit
• b.A sheet metal shroud installed around the whole burner compartment
• c.A barrier such as bollards to protect it from vehicle impact✓
• d.A secondary drain pan under the entire cabinet

Where an appliance is subject to vehicle damage, physical protection such as pipe bollards or a curb must be provided. A shroud around the burner does nothing to stop a car. A drain pan addresses condensate overflow, a different failure. And smoke detection is an alarm function that does not prevent the impact.California Mechanical Code (Title 24, Part 4)

You are brazing a suction line with nitrogen flowing through the tubing. What flow condition is correct?

• a.Full cylinder pressure with the regulator removed for speed
• b.No flow during heating and a purge afterward to clear smoke
• c.A high-pressure blast to cool the joint while it solidifies
• d.A low, steady trickle just sufficient to displace the air✓

A gentle continuous flow sweeps oxygen out so no copper oxide scale forms inside the tube, without blowing the molten alloy out of the joint. A high-pressure blast chills the joint and prevents the filler from flowing. Purging only after the fact leaves scale already formed inside the line. And running unregulated cylinder pressure into thin-wall tubing risks rupture and injury.

Why does copper oxide scale inside a refrigerant line matter after the system is running?

• a.It causes the compressor windings to short to the shell
• b.It reacts with the refrigerant to raise system operating pressure
• c.It raises the copper's thermal conductivity and overcools the line
• d.It breaks loose and plugs the metering device and filter drier✓

Flakes of scale travel with the refrigerant and lodge in the smallest passages, restricting the metering device and loading the drier. Scale insulates rather than improving conductivity. It is chemically inert in the refrigerant and does not raise pressure by reaction. And a winding short is an electrical failure that loose scale in the refrigerant circuit does not cause.

A new line set has been brazed. What is the correct order of the next two steps?

• a.Pressure test for leaks, then evacuate to a deep vacuum✓
• b.Release the factory charge, then pressure test the joints
• c.Evacuate to a deep vacuum, then pressure test for leaks
• d.Start the system briefly, then evacuate while it runs

Leaks are found with pressure because a vacuum cannot push anything out for a detector to find, so testing precedes evacuation. Evacuating first wastes the pump run if a joint leaks. Releasing refrigerant to test is venting and is prohibited. And running a compressor under vacuum can damage the motor and pull air and moisture into the system.

What gas should be used to pressure test a newly brazed refrigerant line set?

• a.Dry nitrogen through a regulator with a relief valve✓
• b.A small charge of system refrigerant boosted with air
• c.Compressed shop air through an inline dryer
• d.Oxygen from the brazing cart at reduced pressure

Dry nitrogen is inert and moisture free, and a regulator with a relief device keeps test pressure below the weakest component's limit. Shop air carries moisture and oil even through a dryer. Oxygen under pressure with oil residue can ignite violently and must never touch a refrigeration system. And mixing refrigerant with air creates a mixture that cannot be recovered and can become combustible.

Where should the TXV sensing bulb be mounted on a suction line larger than 7/8 inch?

• a.On the side of the horizontal line at about four or eight o'clock✓
• b.On the underside of the line at the six o'clock position
• c.Anywhere on the vertical suction riser above the evaporator coil outlet
• d.On the top of the horizontal line at the twelve o'clock position

On larger lines the bulb goes on the side, clear of the oil that runs along the bottom and clear of the vapor stratification at the top, so it reads a representative temperature. The top position reads vapor that may not represent the true suction condition on a large line. The bottom position reads the oil film and gives a false low reading. And a vertical riser can hold refrigerant and oil unpredictably, so the bulb belongs on a horizontal run.

A split system has the condenser 20 feet above the evaporator. What is the main piping consideration?

• a.The suction line must be reduced one size to raise velocity
• b.Vertical lift adds pressure loss in the liquid line, reducing subcooling✓
• c.The line set must include a receiver at the base of the riser
• d.The liquid line must be insulated to prevent flash gas

Lifting liquid refrigerant costs static head, and that pressure drop consumes subcooling and can produce flash gas at the metering device. Insulation on a liquid line is sometimes used in hot locations but does not counteract static lift. Reducing suction line size raises velocity but also raises pressure drop and hurts capacity. And residential split systems do not normally carry a receiver, so adding one is not the standard remedy.

The evaporator sits above the condenser and the suction riser is 25 feet tall. What piping detail helps oil return?

• a.A properly formed trap at the base of the riser✓
• b.A check valve installed at the midpoint of the riser
• c.Oversizing the suction riser by two pipe sizes
• d.A liquid line trap at the top of the riser

A trap at the bottom of a suction riser collects oil until refrigerant velocity carries it up as a slug. A trap belongs in the vapor line, not the liquid line, where liquid flows continuously anyway. Oversizing the riser lowers velocity and makes oil return worse, not better. And a check valve blocks reverse flow but does nothing to lift oil against gravity.

Which line-set error most commonly causes low suction pressure and poor capacity on a long run?

• a.Using long-radius bends instead of tight elbows
• b.Insulating the suction line with too thick a wall
• c.Running the line set inside conditioned space
• d.Using a suction line one size smaller than the manufacturer specifies✓

An undersized suction line adds pressure drop over the whole run, lowering pressure at the compressor and cutting mass flow and capacity. Thicker insulation reduces heat gain, which helps rather than hurts. Long-radius bends reduce pressure loss compared with tight elbows. And routing inside conditioned space lowers heat gain to the suction line, again a benefit.

A liquid line filter drier is installed backwards on a cooling-only split system. What is the likely result?

• a.Filtered debris can wash off the outlet screen and reach the metering device✓
• b.The drier will not absorb any moisture from the refrigerant
• c.The system will operate normally, because refrigerant flow direction does not matter
• d.The compressor will run backwards on the next start

A drier's screen and filter media are arranged for one direction; reversed, trapped particles are flushed downstream toward the metering device. The desiccant still adsorbs moisture regardless of direction, so that is not the failure. Compressor rotation is set by the motor and the electrical supply, not by drier orientation. And a bidirectional drier exists precisely because ordinary driers are direction sensitive.

An air handler is installed in an attic above finished ceilings. What condensate provision is normally required?

• a.A single primary drain sloped at least one inch per foot
• b.A gravity drain discharging onto the roof surface directly beneath the unit
• c.An auxiliary drain pan with its own drain or a water-level shutoff device✓
• d.A condensate pump discharging into the nearest plumbing vent

Equipment above a finished space needs secondary protection, provided by an auxiliary pan with a separate drain or by a switch that shuts the equipment off when water rises. A pump may be used for the primary drain but does not by itself satisfy the secondary protection requirement. A single primary drain provides no backup when it clogs, and a one-inch-per-foot slope is far steeper than the usual requirement. And discharging condensate onto a roof is not an approved point of disposal.California Mechanical Code (Title 24, Part 4)

Why does a draw-through cooling coil require a trap in its condensate drain?

• a.The trap is required only when the drain runs uphill to a sink
• b.The trap raises the water level so the pan drains faster
• c.The trap prevents refrigerant vapor from escaping through the drain
• d.The drain is under negative pressure, and without a trap air is pulled in instead of water out✓

In a draw-through arrangement the pan sits on the suction side of the blower, so the drain outlet is negative and a water seal is needed for the pan to actually empty. A trap does not increase drainage speed; it enables it. Refrigerant is inside sealed tubing and never reaches the condensate pan. And a drain line should never run uphill under gravity, trapped or not.

A condensate drain line is run with several sags where it crosses the attic. What symptom should you expect?

• a.The blower will draw excessive amperage
• b.The compressor will trip on high head pressure
• c.Water will back up and the safety switch will shut the unit off✓
• d.The coil will freeze on long cooling cycles

Standing water in a sagging line restricts flow and eventually backs up into the pan, tripping the float switch or overflowing. Coil freezing is caused by low airflow or low charge, not by drain routing. Blower amperage responds to static pressure and wheel condition. And head pressure is a refrigerant-side condition unaffected by where the drain sags.

Where may condensate from a residential cooling coil generally be discharged?

• a.Onto the ground directly beneath the outdoor condenser
• b.Into the crawl space provided a vapor barrier is already present
• c.Into a vent pipe serving a plumbing fixture
• d.To an approved location such as an indirect waste receptor✓

Condensate is treated as an indirect waste and must go to an approved receptor or point of disposal that prevents contamination and nuisance. Discharging into a plumbing vent obstructs the vent and violates its function. Random ground discharge under equipment creates a nuisance and can undermine the pad. And crawl-space discharge introduces continuous moisture under the building regardless of a ground cover.California Mechanical Code (Title 24, Part 4)

A furnace in an attic requires an unobstructed passageway to reach it. What else is normally required at the equipment?

• a.A ceiling-mounted smoke detector inside the enclosure
• b.A window or roof hatch within six feet of the appliance
• c.A fire extinguisher mounted within reach of the platform
• d.A level working platform, permanent lighting, and a receptacle outlet✓

Attic equipment must be reachable and serviceable, which means a solid working platform in front of the unit plus a light and a convenience receptacle for service tools. Smoke detection in the attic enclosure is not the servicing requirement. A mounted extinguisher is a good practice but is not what the access provisions call for. And no window or hatch adjacent to the appliance is required by the access rules.

You are setting an outdoor condensing unit on a new concrete pad. How should the pad be prepared?

• a.On loose topsoil so the pad can settle evenly with the surrounding ground
• b.Elevated on wood blocking to isolate it from ground moisture
• c.On compacted, well-drained soil so the unit stays level over time✓
• d.Sloped at least two inches toward the house for drainage

A pad on firm, drained subgrade keeps the cabinet level, which protects compressor oil return and proper condensate and fan operation. Loose topsoil settles unevenly and tips the unit. Sloping toward the house directs runoff at the foundation and tilts the equipment. And untreated wood blocking rots and shifts, leaving the unit unsupported.

A condenser is being installed 6 inches from a solid fence on the coil side. What is the practical consequence?

• a.The unit will short cycle on the low-pressure control
• b.Recirculated hot discharge air raises head pressure and cuts capacity✓
• c.The compressor will lose oil because of restricted suction
• d.The fan motor will overheat from a lack of ventilation air

Blocking airflow to a condenser coil forces the unit to re-ingest its own hot air, driving condensing temperature and head pressure up and capacity down. Fan motors on these units are cooled by the air they move and rarely fail first from tight clearance. Oil return is a piping and velocity issue, not a clearance issue. And low-pressure trips come from loss of charge or airflow on the indoor side.

Where must the disconnecting means for an outdoor air-conditioning condenser be located?

• a.Directly below the unit, within 12 inches of the pad
• b.Within sight of and readily accessible from the equipment✓
• c.Inside the building at the electrical panel serving the circuit
• d.Anywhere on the property provided it is padlocked

A technician working on the unit must be able to see and reach the disconnect, so it is installed within sight and readily accessible. A panel inside the house may be out of sight of the outdoor unit, allowing someone to re-energize it. A remote lockable disconnect alone does not satisfy the within-sight rule for this equipment. And there is no requirement fixing it a foot below the unit, which would also expose it to water and debris.California Electrical Code (Title 24, Part 3)

Low-voltage thermostat wire is being run alongside the line-voltage feeder in the same attic. What practice should be followed?

• a.Twist the two cables together so they support each other across the joists
• b.Run both inside the same flexible conduit for neatness
• c.Splice the low-voltage cable to the equipment ground for shielding
• d.Keep the classes separated and support the low-voltage cable independently✓

Class 2 control wiring is separated from line-voltage conductors and supported on its own so induced noise and insulation damage are avoided. Twisting them together puts the two classes in continuous contact. Sharing a raceway mixes voltage classes in a way the electrical code restricts. And connecting a control conductor to the equipment ground short-circuits the control circuit rather than shielding it.

On a conventional residential low-voltage control system, which terminal energizes the compressor contactor on a cooling call?

• a.W
• b.R
• c.Y✓
• d.G

The Y terminal carries the cooling call from the thermostat to the contactor coil at the condensing unit, which then closes and starts the compressor and condenser fan. W energizes the heat source, whether that is the gas valve circuit on a furnace or the sequencers on electric heat. G energizes the indoor blower independently of any heating or cooling call. And R is the transformer hot side that feeds all of the other calls rather than being a call itself.

A heat pump is installed with electric strip heat. How should the strip heat be controlled to protect efficiency?

• a.Wired directly to the W terminal in place of the compressor
• b.Energized with every heating call so recovery is fast
• c.Staged on only when the heat pump cannot satisfy the call✓
• d.Controlled by the outdoor fan relay so it follows defrost only

Auxiliary heat is a supplement, so controls bring it on only when the compressor falls behind or during defrost. Energizing it on every call wastes the heat pump's efficiency advantage entirely. Wiring it to W in place of the compressor turns an expensive heat pump into an electric furnace. And tying it only to the outdoor fan relay leaves the house without backup on the coldest hours.

Where should a wall thermostat be mounted in a typical residence?

• a.On an interior wall in a frequently used room, away from drafts and sun✓
• b.In the kitchen so cooking heat is detected quickly
• c.Directly above a supply register so it senses delivered air
• d.On an exterior wall near a window so it senses outdoor temperature swings

A thermostat should read average conditions in the living space, which means an interior wall in a used room and clear of sun, drafts, and appliance heat. An exterior wall conducts outdoor temperature into the sensor and gives false readings. A kitchen sees cooking heat that has nothing to do with the rest of the house. And mounting over a register makes the thermostat measure supply air and short cycle the equipment.

A furnace is installed in a downflow configuration on a combustible floor. What is required?

• a.Sheet metal flashing extending 12 inches beyond the cabinet
• b.A listed floor base or subbase approved for that furnace✓
• c.A two-inch air gap between the cabinet and the finished floor
• d.A layer of unfaced fiberglass insulation under the cabinet

Downflow furnaces discharge hot air through the floor, so the manufacturer's listed base or an approved subbase is required to protect the combustible construction. An arbitrary air gap is not a listed assembly. Loose flashing does not carry a listing and does not create the required clearance. And fiberglass under the cabinet is neither listed nor structurally suitable for the equipment.

What does the clearance to combustibles marked on a furnace rating plate represent?

• a.The minimum tested separation between the cabinet and combustible material✓
• b.The recommended distance for airflow around the cabinet
• c.The space needed in front of the unit to service the blower
• d.The distance the vent must be kept from the roof deck

Clearance to combustibles is a listed, tested distance that keeps adjacent wood and other combustible materials below their ignition temperature. Service clearance is a separate dimension driven by access to components. Vent clearances are specified for the vent system, not the cabinet. And it is a minimum safety requirement, not an airflow recommendation the installer may adjust.

Gas piping to a new furnace is being sized. Which set of inputs governs the pipe size?

• a.The total connected input BTU, the developed length, and the gas pressure✓
• b.The number of elbows and the diameter of the existing meter
• c.The furnace efficiency rating and the total number of appliances in the house
• d.The furnace output BTU and the length of the vent run

Gas pipe sizing tables are entered with the demand in BTU input, the developed length to the furthest outlet, and the supply pressure and allowable pressure drop. Output BTU understates the fuel actually drawn, and the vent run is irrelevant to gas sizing. Fittings are usually accounted for in the length allowance rather than counted individually against a meter diameter. And efficiency affects output, not the input the pipe must deliver.California Mechanical Code (Title 24, Part 4), Chapter 13

What is the correct arrangement for a sediment trap at a gas furnace?

• a.A horizontal extension of pipe upstream of the shutoff valve
• b.A flexible connector looped below the appliance inlet
• c.A capped vertical leg downstream of the shutoff and ahead of the appliance✓
• d.A capped tee installed above the gas valve inlet

The trap is a tee with a capped drop leg placed after the shutoff and before the appliance, so debris and moisture fall out of the gas stream by gravity. A horizontal extension gives particles no place to settle. A leg above the valve inlet works against gravity and traps nothing. And a looped flexible connector is not a sediment trap and may violate the connector's listing.

A flexible appliance connector is used to attach a furnace to the gas piping. Which practice is correct?

• a.Join two connectors together to reach the appliance
• b.Use one connector of adequate length without passing it through a wall✓
• c.Route the connector through a knockout hole in the furnace cabinet panel
• d.Conceal the connector inside the framed wall for appearance

A listed connector is used singly, in the open, and must not penetrate walls, floors, or appliance panels where it cannot be inspected or where it can chafe. Coupling two connectors together is specifically prohibited. Passing it through a cabinet panel exposes it to sharp edges and heat. And concealing it in a wall makes leak inspection impossible.

A furnace gas shutoff valve is being installed. Where does it belong?

• a.At the gas meter only, so one valve serves the whole house
• b.Downstream of the appliance regulator inside the cabinet
• c.In the attic above the furnace where it stays out of the way
• d.In the same room, ahead of the connector and within reach of the appliance✓

Each appliance gets an accessible shutoff in the same room, upstream of the connector, so gas can be isolated at the equipment. Putting it in an attic above a first-floor furnace defeats accessibility. Inside the cabinet downstream of the regulator it cannot isolate the appliance for service. And a meter valve alone shuts down the entire building rather than the one appliance.

After connecting gas piping to a new furnace, how should the joints be checked?

• a.Watch the gas meter dial for one minute with all other appliances running
• b.Hold a lit match near each joint and watch for flare-up
• c.Feel each joint by hand for the cold spot a leak produces
• d.Apply an approved leak detection solution or use an electronic detector✓

Approved bubble solution or a calibrated combustible gas detector finds leaks safely and precisely at each joint. An open flame at a suspected leak is an ignition source and is never an acceptable test. A leak large enough to feel is far beyond an acceptable one, and small leaks give no tactile clue. And watching the meter with appliances running cannot distinguish normal consumption from a leak.

Corrugated stainless steel tubing is used for a gas line to a rooftop unit. What additional installation step is commonly required?

• a.Supporting the tubing at intervals of no greater than 24 inches apart
• b.Bonding the tubing system per the manufacturer and electrical code✓
• c.Applying a corrosion-inhibiting coating to the jacket
• d.Sleeving the entire run in schedule 40 PVC

Corrugated stainless steel tubing is required to be electrically bonded to reduce the risk of damage from a lightning-induced arc. PVC sleeving is used for specific buried or penetration conditions, not as a general requirement. The factory jacket is the corrosion protection and is not field coated. And support spacing for this tubing follows the manufacturer's listing, which is generally more generous than two feet.

Sheet metal duct joints on a new supply trunk are being sealed. Which method is acceptable under current practice?

• a.Mastic applied over the joint, reinforced with mesh at wide gaps✓
• b.Silicone caulk applied only to the outside corners of the joint
• c.Standard cloth-backed duct tape wrapped twice around the joint
• d.Sheet metal screws alone, spaced no more than four inches apart at each seam

Mastic, with embedded mesh where the gap is wide, forms a durable air seal that stays flexible through thermal cycling. Cloth-backed duct tape dries out and releases, which is why it is not accepted for duct sealing. Silicone at corners leaves the seam itself unsealed. And screws are mechanical fasteners; they hold the joint but do not seal it.

How should flexible duct be supported between structural members in an attic?

• a.With wide straps at the manufacturer's spacing, limiting sag between supports✓
• b.By resting it directly on top of the ceiling insulation along its whole length
• c.With narrow wire ties every ten feet to allow natural sag
• d.With plastic strapping pulled tight enough to compress the liner

Flex duct is supported by straps wide enough not to pinch the liner, spaced per the manufacturer, with sag held to a small fraction of the span. Narrow wire ties cut into the jacket and create a restriction at each support. Laying the duct on insulation allows long uncontrolled sags and crushes the liner where it rests. And tight strapping that compresses the duct throttles airflow at every support point.

A flexible connector is installed between the air handler and the supply plenum. What is its purpose?

• a.To break the transmission of blower vibration into the duct system✓
• b.To relieve excess static pressure during blower startup
• c.To act as an access point for cleaning the supply trunk
• d.To provide an expansion joint for thermal movement of the sheet metal plenum

A canvas or listed flexible connector isolates blower vibration so it is not carried structurally into the ductwork and the building. Sheet metal duct does not need an expansion joint over these temperature ranges. It is not an access panel and should not be opened for cleaning. And it is airtight, so it does not relieve pressure at any point in the cycle.

A return duct is being installed in a two-story house. Which location must be avoided as a source of return air?

• a.A central second-floor hallway ceiling
• b.A living room wall about six feet above the finished floor
• c.A first-floor family room with a high ceiling
• d.A furnace closet containing a fuel-burning appliance✓

Taking return air from a room containing a fuel-burning appliance can depressurize that space and pull flue gases into the airstream. A second-floor hallway is a common and acceptable return location. A living room wall return is standard practice. And a family room with high ceilings is a normal return location, sometimes with a high and low grille for stratification.

Why is a building cavity such as a stud bay or panned floor joist no longer acceptable as a return duct in new work?

• a.It leaks to unconditioned space and cannot be sealed or verified✓
• b.It produces excessive velocity because the free area is too small
• c.It prevents the use of a washable filter at the grille
• d.It cannot be insulated to any R-value at all

Framing cavities communicate with wall, attic, and crawl spaces, so a negative-pressure return pulls in dust, moisture, and combustion products and cannot pass a leakage test. Free area in a stud bay is often generous, so velocity is not the core problem. Cavities can be lined, though poorly, so total inability to insulate overstates it. And filter type at the grille is unrelated to whether the cavity is sealed.

A supply duct passes through a rated fire wall in a small commercial building. What is generally required at the penetration?

• a.A volume damper set to the design airflow
• b.A listed fire damper installed per its listing✓
• c.A backdraft damper oriented with the airflow direction
• d.A flexible connector to allow movement

A listed fire damper installed with the required sleeve and retaining angles restores the rating of the assembly when duct penetrates it. A volume damper balances airflow and has no fire rating. A backdraft damper prevents reverse airflow and likewise carries no rating. And a flexible connector is a vibration break, which would actually be a weak point in a rated barrier.

Balancing dampers are being installed on a new branch duct system. Where should they be placed?

• a.Behind each register face where they can be adjusted from the room
• b.At the takeoff from the trunk, accessible for adjustment✓
• c.At the midpoint of each flexible branch inside the insulation
• d.Immediately downstream of the coil in the supply plenum

Dampers at the takeoff throttle the branch at its source, keeping generated noise well upstream of the occupied room and leaving the handle accessible. Register dampers make noise right at the occupant's ear and disturb the throw pattern. A damper buried mid-run in flex cannot be reached for balancing. And a single damper at the plenum throttles everything at once instead of balancing branches against each other.

A new air handler will use a 4-inch media filter instead of a 1-inch filter. What must the installer verify?

• a.That the return grille is at least twice the filter's face area
• b.That the filter media is replaced on the same schedule as a 1-inch pleated filter
• c.That the filter is installed on the discharge side of the blower
• d.That the cabinet has room for the rack and the blower can handle the drop✓

A deeper media filter needs physical space for a sealed rack and adds a pressure drop the blower must absorb without falling below design airflow. There is no rule requiring the return grille to be double the filter area. Filters belong upstream of the blower and coil so both stay clean. And a 4-inch media filter's whole advantage is a much longer service interval, so matching the 1-inch schedule is wrong.

A ductless mini-split indoor head is being mounted. What installation detail most affects condensate handling?

• a.The head must be mounted at least seven feet above the finished floor line
• b.The drain line must maintain continuous fall from the head to the outlet✓
• c.The line set must enter the wall below the level of the drain
• d.The head must be mounted level side to side within one degree

Mini-split heads drain by gravity through a small hose, so any rise or sag in that hose backs water into the pan and out the front of the unit. Mounting height affects throw and appearance but not drainage. The line set penetration is normally made below the head with the drain running alongside; its exact position relative to the drain is not the governing factor. And heads are typically pitched slightly toward the drain rather than dead level.

A multi-head mini-split system is being commissioned. Why does the manufacturer specify additional refrigerant beyond the factory charge?

• a.Because the outdoor unit ships with a partial charge only
• b.Because each indoor head must be individually pumped down
• c.Because multiple indoor heads increase the compressor's oil requirement
• d.Because line set length beyond a base allowance adds internal volume✓

The factory charge covers the outdoor unit plus a stated line length, and every foot beyond that adds volume that must be filled with refrigerant. Oil charge is handled separately by the manufacturer's oil specification. The units ship with a full charge for the base condition, not a partial one. And pumping down individual heads is a service procedure, not the reason for a charge adjustment at startup.

A rooftop packaged unit is being set on a new curb. What is the curb's primary function?

• a.To provide a weathertight, structurally supported transition for duct and unit✓
• b.To raise the unit above the parapet for better airflow
• c.To isolate the electrical supply from the roof membrane
• d.To serve as the required service platform around the unit

The curb ties into the roof structure and membrane, supports the unit, and forms the sealed opening through which supply and return ducts pass. Parapet height is unrelated to the curb's purpose. Electrical isolation is achieved with proper raceway and supports, not the curb. And service clearance around the unit is provided on the roof surface, not by the curb itself.

Equipment is being installed on a commercial roof more than 16 feet above grade. What access provision is normally required?

• a.A rope-and-anchor system at the parapet edge
• b.A roof hatch located within ten feet of the unit's main control panel
• c.A portable ladder stored on the roof next to the unit
• d.A permanent means of access such as a fixed stair or listed ladder✓

Rooftop appliances above the height threshold require a permanent, code-compliant means of access so service can be performed safely. A portable ladder is not a permanent means and can be removed or misused. Fall arrest anchors address edge work, not the climb to the roof. And there is no ten-foot hatch proximity requirement tied to the control panel.

A rooftop unit's economizer is being installed. What does the outdoor air damper control accomplish?

• a.It relieves supply duct static pressure during startup
• b.It uses cool outdoor air for free cooling when conditions allow✓
• c.It maintains a fixed minimum position at all times to reduce cycling
• d.It increases condenser airflow during high ambient operation

An economizer modulates outdoor air to meet the cooling load mechanically-free when the outdoor air is suitable, saving compressor run time. A fixed minimum position is only the ventilation floor, not the economizer's function. Condenser airflow is set by the condenser fan, which the economizer does not control. And static pressure relief is a barometric or powered relief function, not the economizer damper's purpose.

An energy recovery ventilator is added to a residence. Where should its exhaust intake be taken from?

• a.The attic, where the warmest air collects in winter
• b.The furnace closet, so appliance heat is recovered
• c.Rooms with the highest moisture and odor loads, such as baths and laundry✓
• d.The garage, where the air is already unconditioned

An ERV pulls stale air from the wettest, most polluted rooms and transfers its energy to incoming fresh air. Drawing from a garage would move vehicle exhaust and stored chemicals through the ventilator. Pulling from an appliance closet can depressurize it and interfere with venting. And attic air is outside the envelope, so exhausting it recovers nothing and only wastes fan energy.

A whole-house exhaust fan for continuous ventilation is being installed in a bathroom. Which specification matters most?

• a.The maximum speed setting listed on the fan carton
• b.The number of blades on the impeller wheel
• c.The rated airflow and sound level at the intended continuous setting✓
• d.The color and style of the ceiling grille

A fan that runs continuously must deliver its required CFM against real duct resistance and be quiet enough that occupants leave it on. The maximum boost setting is not the condition it will operate at. Grille appearance has no effect on ventilation performance. And blade count is a design detail that says nothing about rated flow or sound.

A bathroom exhaust duct is terminated in the attic instead of through the roof or wall. What is the consequence?

• a.The duct will collapse from the negative pressure it creates
• b.The exhaust airflow will exceed its rating without a proper termination
• c.Moisture is discharged into the attic, causing condensation and mold✓
• d.The fan will trip on thermal overload from backpressure

Exhaust must be carried to the outdoors, and dumping humid air into a cold attic condenses it on sheathing and framing. Backpressure at an open discharge is actually lower, not higher, so overload is not the issue. Airflow does not exceed the fan's rating simply because the duct is short. And an exhaust duct is under positive pressure downstream of the fan, so it does not collapse.

A supply register is being located in a bedroom in a cold California climate zone. Where does it generally perform best?

• a.Behind the door swing where it will not be blocked by furniture
• b.Near the exterior wall so the airstream washes the cold surface✓
• c.In the interior wall closest to the return grille
• d.In the ceiling directly above the bed for the shortest throw

Placing the supply at the perimeter lets the airstream counteract downdraft and cold radiation from windows and exterior walls. A register next to the return short-circuits supply air straight back to the system. Directly over the bed creates a draft complaint and does not address the cold surfaces. And behind the door swing is a location chosen for convenience, which usually blocks or misdirects the throw.

You are replacing a coil in an existing furnace cabinet. What matching issue must be verified?

• a.That the coil is rated for at least one ton more than the condenser
• b.That the coil has the same fin spacing as the one removed
• c.That the coil and condenser combination is a listed AHRI match✓
• d.That the coil casing is the same brand as the furnace cabinet

Rated capacity and efficiency apply only to certified combinations, so the coil must be an approved match for that outdoor unit and metering device. Brand matching alone does not guarantee a certified combination. Fin spacing is one design detail among many and does not establish a match. And deliberately oversizing the coil by a ton is not a listed combination and changes the refrigerant balance.

A replacement condenser uses a different refrigerant than the existing indoor coil and line set. What is the correct approach?

• a.Verify manufacturer approval and replace or properly clean the components✓
• b.Charge the new refrigerant into the existing coil and monitor operating pressures
• c.Flush the line set with refrigerant from the recovery machine
• d.Add a larger filter drier and reuse the line set as is

Different refrigerants use different oils and design pressures, so the manufacturer's instructions govern whether existing components may be reused, cleaned, or must be replaced. Simply charging a new refrigerant into an incompatible coil risks oil return failure and pressure problems. A larger drier does not remove incompatible oil from the tubing walls. And using recovered refrigerant as a flushing agent is not an approved cleaning method.

A residential system uses R-454B, an A2L refrigerant. What installation consideration does that class introduce?

• a.The equipment's listed mitigation features and charge limits must be followed✓
• b.The line set must be brazed using a silver-bearing alloy of at least 45 percent
• c.The system may be charged only in the vapor phase from the cylinder
• d.The outdoor unit must be installed at least ten feet from any window

A2L refrigerants are mildly flammable, so listed equipment carries charge limits, leak detection, and mitigation provisions that the installer must not defeat. Brazing alloy selection is driven by the joint and base metals, not by the refrigerant's safety class. Zeotropic blends like R-454B are charged as liquid to preserve composition, so vapor-only charging is wrong. And there is no blanket ten-foot window setback for the outdoor unit.

How should horizontal refrigerant lines be supported along a wall?

• a.By taping them to the adjacent condensate drain line every several feet
• b.Only at each end, allowing the run to hang free in between
• c.At regular intervals with hangers that do not crush the insulation✓
• d.By resting them on the top plate wherever they cross framing

Regularly spaced hangers sized to the tubing keep the lines from sagging and vibrating while leaving the insulation intact and continuous. Taping to a drain line transfers vibration and offers no real support. Resting tubing on framing lets it chafe and work-harden at each crossing. And supporting only the ends allows sag, vibration fatigue, and eventual joint failure.

Why is the suction line insulated on a split system while the liquid line usually is not?

• a.The liquid line is already insulated by its higher pressure
• b.Insulation on the suction line increases refrigerant velocity
• c.The cold vapor line would gain heat and sweat onto the building✓
• d.Insulation prevents the suction line from vibrating against framing

Suction vapor is below the dew point of surrounding air, so uninsulated tubing collects condensation and also picks up heat that raises superheat at the compressor. Insulation does not change velocity, which is set by mass flow and pipe area. Pressure does not insulate anything. And while insulation may cushion contact, vibration is controlled with proper supports rather than by wrapping the line.

A technician makes a flare connection on a mini-split service valve. Which practice produces a reliable joint?

• a.Overtighten the nut until the copper tubing visibly deforms against the seat
• b.Apply pipe dope to the flare face before tightening the nut
• c.Reuse the original flare from the removed unit to save time
• d.Deburr the tube, form a clean flare, and torque the nut to specification✓

A clean, properly formed flare tightened to the manufacturer's torque value seals metal to metal without cracking the copper. Overtightening splits the flare or extrudes it, creating a leak that appears later. Pipe dope is not a sealant for a flare fitting and can contaminate the system. And a previously compressed flare has already work-hardened and will not reseal reliably.

The service valves on a new condenser are still front-seated after the line set is connected and evacuated. What must happen next?

• a.Crack the liquid valve only and leave the suction valve closed
• b.Start the system and open the valves once suction pressure stabilizes
• c.Leave them closed so the factory charge stays isolated for shipping
• d.Open the valves fully to release the factory charge into the system✓

Once the line set and coil are leak tested and evacuated, both valves are opened fully so the factory charge fills the whole circuit. Starting a compressor with the valves closed runs it into a vacuum and can damage the motor. Leaving them closed means the system has no refrigerant available at all. And opening only the liquid valve starves the compressor while flooding the low side.

What vacuum level is generally accepted as the target before charging a new residential split system?

• a.5,000 microns held for one minute
• b.2,000 microns held for five minutes
• c.500 microns or lower, holding after the pump is isolated✓
• d.29 inches of mercury as read on a compound manifold gauge

A deep vacuum near or below 500 microns, verified by isolating the pump and watching for rise, shows that moisture and non-condensables are actually gone. Readings of 5,000 or 2,000 microns still leave water vapor in the system, and short hold times prove nothing. And a compound gauge lacks the resolution to distinguish 29 inches from a genuinely deep vacuum.

During evacuation the micron gauge falls to 400 but rises to 2,500 and levels off after the pump is valved off. What does that indicate?

• a.Moisture remaining in the system continuing to boil off✓
• b.A leak in the system or at the gauge connections
• c.A correctly evacuated system that is ready to be charged
• d.A vacuum pump with contaminated oil

A rise that stops and levels off means something inside is still vaporizing and then reaches equilibrium, the classic signature of residual moisture. A leak produces a rise that keeps climbing toward atmospheric pressure without leveling. Bad pump oil prevents reaching a deep vacuum in the first place rather than causing a leveling rise. And a system ready to charge holds close to its final reading with only a slight rise.

Why should the vacuum pump be connected with large-diameter hoses and both service ports open?

• a.To keep refrigerant oil from migrating into the pump
• b.To prevent the compressor from rotating during evacuation
• c.To reduce flow restriction so the system can reach a deep vacuum in reasonable time✓
• d.To allow the micron gauge to read pressure on both sides equally

At deep vacuum the gas is extremely thin and small hoses and valve cores choke the flow, stretching evacuation for hours or preventing it entirely. Oil migration is managed by pump design and isolation valves, not hose size. Nothing about hose diameter affects compressor rotation. And the micron gauge should be placed at the system, away from the pump, rather than averaging both sides.

A new system is being charged with a zeotropic blend. How should refrigerant be removed from the cylinder?

• a.As liquid, metered through the gauge set so it flashes before the compressor✓
• b.As liquid drawn directly into the suction service port
• c.As vapor from the top, to avoid slugging the compressor
• d.As vapor after warming the cylinder in hot water

A blend must leave the cylinder as liquid to keep its composition correct, and the technician meters that liquid so it vaporizes before reaching the compressor. Vapor charging a blend removes the more volatile component first and changes the mixture. Warming a cylinder in hot water is a dangerous practice and still charges vapor. And dumping unrestricted liquid into the suction port slugs the compressor.

What is the correct way to determine the final charge on a new TXV split system?

• a.Charge until the suction line sweats back to the compressor
• b.Weigh in the calculated charge, then verify with subcooling✓
• c.Charge to the pressure listed on the condenser's data plate
• d.Charge until superheat reaches ten degrees at the evaporator outlet

Weighing in the factory charge plus the line-length adjustment and then confirming subcooling is the manufacturer-supported method for a TXV system. Sweating on the suction line depends on humidity and tells nothing about charge. Data plates list electrical and capacity data, not a target operating pressure. And superheat is controlled by the TXV itself, so it cannot be used to judge charge on that system.

A crankcase heater is supplied with a new condensing unit installed in a cold climate. When should it be energized?

• a.After the system has reached steady-state operation
• b.Several hours before the compressor is first started✓
• c.Only while the compressor is running under load in cold weather
• d.Only during the defrost cycle on heat pump systems

The heater drives liquid refrigerant out of the oil, so it must run for hours before the first start to prevent a flooded start and oil foaming. Energizing it only while the compressor runs leaves the crankcase cold at the moment of highest risk. Defrost is a heat pump control sequence with a different purpose. And waiting until steady state defeats the entire point of preheating the oil.

A heat pump outdoor unit is being set in a location that gets winter frost. What mounting detail matters most?

• a.Tilting it slightly toward the house so water runs away from the fan
• b.Elevating it on a stand so defrost water drains clear of the coil✓
• c.Enclosing three sides to shield the coil from wind
• d.Setting it directly on grade so defrost water soaks into the soil

Heat pumps shed water during defrost, and elevating the unit keeps that water from refreezing under and into the coil. Sitting on grade lets ice build up around the base and block the bottom of the coil. Enclosing three sides restricts the airflow the outdoor coil depends on. And tilting the cabinet compromises compressor oil return and directs water at the structure.

Two condensing units are installed side by side against a wall. What clearance concern is specific to this arrangement?

• a.The condensate from one unit will drain into the other's base pan
• b.The shared electrical disconnect must be centered between them
• c.The refrigerant line sets must be routed above the units rather than below them
• d.Each unit can ingest the other's discharge air unless spacing is maintained✓

Side-by-side units placed too closely trade hot discharge air, driving both units' head pressure up and capacity down. Each unit requires its own disconnect within sight, so a shared centered device is not the issue. Line routing above or below is an installation preference with no bearing on clearance. And air-conditioning condensers do not produce condensate that could drain into a neighboring unit.

What is the purpose of the equipment ground conductor run with the branch circuit to a condensing unit?

• a.To provide the return path for the low-voltage control circuit at the board
• b.To carry the unbalanced load between the two hot legs
• c.To limit voltage drop over the length of the run
• d.To provide a low-impedance fault path so the overcurrent device opens✓

The equipment ground bonds the metal cabinet and gives fault current a low-impedance path back to the source so the breaker clears the fault quickly. Unbalanced load on a 240-volt appliance circuit is a neutral function, not a ground function. The low-voltage circuit has its own conductors and is isolated from the equipment ground. And voltage drop is managed by conductor size and length, not by the grounding conductor.

The nameplate of a condensing unit lists a maximum overcurrent protection of 35 amps and a minimum circuit ampacity of 22 amps. How should the circuit be built?

• a.Conductors rated at least 22 amps, protected at no more than 35 amps✓
• b.Conductors and breaker both sized to exactly 35 amps
• c.Conductors rated at least 35 amps, protected at 22 amps
• d.Conductors sized to 22 amps with a 60 amp breaker for starting surge

Minimum circuit ampacity sets the conductor size and maximum overcurrent protection caps the breaker, so 22-amp conductors on a breaker no larger than 35 amps is correct. Sizing conductors to the breaker rating and then undersizing the breaker inverts both values. Forcing both to 35 amps ignores the ampacity figure the manufacturer calculated. And a 60-amp breaker exceeds the listed maximum and would not protect the equipment.

A technician finds the new furnace's blower rotating backwards after wiring the three-phase supply to a commercial air handler. What is the fix?

• a.Reverse the low-voltage thermostat wires at the terminal board
• b.Replace the motor with one rated for the opposite rotation
• c.Swap any two of the three line conductors at the disconnect✓
• d.Rewire the motor's internal windings for the other direction

Three-phase rotation is determined by phase sequence, so interchanging any two line conductors reverses the motor. Control wiring does not set rotation direction. Opening a motor to rewire internal windings is not a field procedure for phase rotation. And replacing a perfectly good motor is unnecessary when the correction is a two-wire swap at the disconnect.

A new furnace is installed and the temperature rise measures 30 F against a rating plate range of 40 to 70 F. What adjustment is appropriate?

• a.Reduce blower speed until the rise falls inside the listed range✓
• b.Increase the manifold gas pressure above the rated value
• c.Replace the limit switch with one rated for a lower setpoint
• d.Add restriction at the return duct to raise the system static pressure

Too low a rise means the blower is moving more air than the burner output warrants, so slowing the blower brings the rise into range. Overfiring the burner past its rated manifold pressure is unsafe and voids the listing. Deliberately restricting the return raises static and stresses the blower rather than properly setting speed. And changing the limit switch masks an airflow setting problem while removing a safety margin.

How is manifold gas pressure on a new natural gas furnace verified at startup?

• a.By measuring inlet pressure at the gas valve during standby
• b.By counting the gas meter dial revolutions over one minute
• c.By reading the pressure at the meter with all appliances off
• d.By connecting a manometer to the valve's outlet tap with the burner firing✓

Manifold pressure is measured at the outlet tap of the gas valve while the burner runs, and compared against the rating plate value. Meter pressure with appliances off shows static supply pressure, not manifold pressure. Inlet pressure during standby tells you the supply is present but not what the burner is receiving. And clocking the meter measures input rate, which is a related but separate check.

A high-efficiency furnace is vented through a sidewall. Which termination concern is most important?

• a.Keeping the vent and intake at exactly the same elevation
• b.Maintaining required separation from windows, doors, and air intakes✓
• c.Terminating below grade level so the plume is not visible
• d.Sloping the vent downward so condensate drains out through the terminal

Sidewall terminations must be far enough from openings and intakes that flue gas is not drawn back into the building. Concentric and two-pipe terminations follow the manufacturer's spacing rather than a rule that both be at the same height. The vent slopes back toward the furnace so condensate drains to the appliance, not out the terminal. And terminating below grade invites blockage by snow, leaves, and standing water.

A condensing furnace's condensate is being routed to a drain. Why is a neutralizer sometimes installed?

• a.To filter out combustion particulate before it reaches the sewer line
• b.Because the condensate is acidic and can attack metal drain piping✓
• c.To reduce the volume of condensate produced
• d.To keep the condensate warm enough to prevent freezing

Flue gas condensate is mildly acidic, and a neutralizer raises its pH so it does not corrode metallic drain lines or violate local discharge rules. Nothing about a neutralizer changes how much condensate the appliance makes. It has no heating function and does not prevent freezing. And it is a chemical treatment, not a particulate filter.

A residential air handler is installed in a closet with louvered doors and no dedicated return duct. What problem does this create?

• a.The blower will be starved because louvers restrict airflow
• b.The closet will be pressurized, forcing air into the wall cavities
• c.Return air is drawn from the closet and whatever leaks into it, bypassing the filter path✓
• d.The equipment cannot be serviced because the doors must remain closed

Using the closet itself as a return plenum pulls air from wall cavities, the attic, and any adjacent unconditioned space, which defeats filtration and duct leakage control. Louvers are usually generous enough that raw restriction is not the primary failure. The closet goes negative on the return side, not positive. And serviceability is a separate concern that door louvers do not create.

When is a mechanical permit generally required for HVAC work in California?

• a.Only when the equipment capacity increases over the original
• b.Only for commercial buildings, since dwellings are exempt
• c.Only when the building's electrical service is also being upgraded at the same time
• d.For installation, replacement, or alteration of equipment and duct systems✓

Local jurisdictions require a mechanical permit for installing, replacing, or altering regulated equipment and ductwork, regardless of building type. Electrical work has its own permit and is not the trigger for the mechanical one. Dwellings are squarely covered by the mechanical code. And a like-for-like change-out still requires a permit even when capacity does not change.California Mechanical Code (Title 24, Part 4)

A technician reads 118 psig suction on an R-410A system whose saturation temperature at that pressure is 40 F, and the suction line measures 52 F. What is the superheat?

• a.8 degrees
• b.12 degrees✓
• c.40 degrees
• d.52 degrees

Superheat is the line temperature minus the saturation temperature, or 52 minus 40, which is 12 degrees. The 8-degree figure would require a line temperature of 48 F. The 40-degree figure is the saturation temperature itself, not a difference. And 52 degrees is the raw line temperature with no subtraction performed at all.

Why is superheat measured at the compressor rather than at the evaporator outlet when checking for flooding?

• a.Because line heat gain means a coil with proper superheat can still return liquid✓
• b.Because the TXV bulb interferes with a reading at the coil
• c.Because the evaporator outlet is inaccessible on most equipment
• d.Because compressor superheat is always lower than evaporator superheat

Total superheat at the compressor accounts for heat picked up along the suction line, and it is the only reading that proves vapor and not liquid is reaching the compressor. Evaporator outlet ports exist on most equipment, so accessibility is not the reason. The sensing bulb reads temperature and does not obstruct measurement. And compressor superheat is normally higher than evaporator superheat because the line adds heat.

A system shows 2 degrees of subcooling and 25 degrees of superheat with a TXV metering device. What is the most likely condition?

• a.The condenser fan is running backwards
• b.The system is overcharged
• c.Airflow across the evaporator is too high
• d.The system is undercharged✓

Low subcooling means the condenser cannot fill with liquid and high superheat means the TXV is starved, and the combination points to a shortage of refrigerant. An overcharge would show high subcooling instead. Excess evaporator airflow raises suction pressure and superheat somewhat but does not empty the condenser. And a reversed condenser fan would drive head pressure and subcooling up, not down.

Which reading tells a technician the most about charge level on a system with a thermostatic expansion valve?

• a.Liquid line subcooling✓
• b.Evaporator superheat
• c.Discharge line temperature
• d.Suction line temperature

A TXV holds superheat nearly constant by design, so subcooling at the liquid line is the reading that responds to how much refrigerant is in the system. Superheat is exactly what the valve is regulating, which makes it insensitive to charge. Suction line temperature alone has no pressure reference. And discharge temperature responds mostly to compression ratio and return gas condition.

A fixed-orifice system is being charged on a hot day. Which method does the manufacturer specify?

• a.Match measured superheat to the target from the charging chart✓
• b.Charge until the sight glass in the liquid line clears
• c.Adjust until subcooling reaches 10 to 12 degrees
• d.Weigh in the nameplate charge without any field verification afterward

A fixed orifice cannot regulate flow, so superheat varies with load, and the target superheat chart based on indoor wet bulb and outdoor dry bulb is the correct field method. Weighing alone is valid only when the entire charge is removed and the line length is known. Subcooling is the TXV method and is not the primary check on an orifice system. And residential split systems rarely have a sight glass to read.

A system has a condensing saturation temperature of 120 F and a liquid line temperature of 118 F on a 95 F day. What does that suggest?

• a.An overcharge that is backing liquid into the condenser tubes
• b.A restricted metering device holding back liquid
• c.Normal operation with a healthy liquid seal
• d.A shortage of refrigerant or poor condenser heat rejection✓

Only 2 degrees of subcooling means the condenser is not filling with liquid, which points to low charge or a condenser that cannot reject heat. A healthy system on that day would show roughly 8 to 15 degrees of subcooling. Overcharge produces high subcooling because liquid stacks in the condenser. And a restriction downstream of the condenser would raise subcooling, not lower it.

What physical change occurs in the refrigerant as it passes through the metering device?

• a.Liquid absorbs heat and boils completely into saturated vapor there
• b.Vapor is compressed into a high-pressure liquid
• c.Superheated vapor is desuperheated and condensed
• d.Pressure drops sharply and part of the liquid flashes to vapor✓

The metering device creates a large pressure drop, and the liquid's own heat boils a fraction of it instantly, chilling the mixture entering the evaporator. Compression to high pressure is the compressor's job. Complete boiling into vapor happens across the evaporator, downstream of the metering device. And desuperheating and condensing occur in the condenser on the high side.

Why does subcooling matter at the inlet to the metering device?

• a.It lowers the compressor's discharge temperature directly
• b.It reduces the superheat the evaporator must produce
• c.It ensures a solid column of liquid so the device meters at its rated capacity✓
• d.It prevents oil from separating out of the refrigerant

A metering device is rated for liquid, and vapor bubbles in the feed reduce mass flow and starve the evaporator, so subcooling guarantees liquid arrives. Discharge temperature is governed mainly by compression ratio and suction superheat. Evaporator superheat is set by the metering device's control action, not by subcooling. And oil circulation depends on velocity and miscibility, not on liquid subcooling.

Which three forces act on a conventional thermostatic expansion valve diaphragm?

• a.Bulb pressure, evaporator pressure, and spring pressure✓
• b.Liquid line pressure, superheat, and subcooling
• c.Discharge pressure, suction pressure, and crankcase oil pressure
• d.Condenser pressure, ambient pressure, and spring force

The bulb's pressure opens the valve, while evaporator pressure and the adjustable superheat spring close it, and the balance sets superheat. Discharge and oil pressures act elsewhere in the system and never reach the diaphragm. Ambient pressure is not a control input to the valve. And superheat and subcooling are conditions, not forces acting on a diaphragm.

What is the purpose of the external equalizer line on a TXV?

• a.To limit the maximum operating pressure the valve will allow
• b.To return oil from the evaporator to the compressor
• c.To bleed pressure from the high side into the evaporator coil at every shutdown
• d.To sense pressure at the evaporator outlet, correcting for coil pressure drop✓

An external equalizer reports the pressure at the coil outlet so the valve controls superheat correctly despite pressure drop through a distributor and long circuits. Pressure equalization at shutdown is done by a bleed-type metering device or a hard start component, not this line. Oil returns through the suction line with refrigerant velocity. And maximum operating pressure limiting is a separate MOP charge feature.

A TXV is hunting, with suction pressure swinging every 30 seconds. Which cause should be checked first?

• a.A loose or poorly insulated sensing bulb✓
• b.A compressor with worn suction valves
• c.A partially blocked outdoor condenser coil
• d.An undersized liquid line filter drier

A bulb that is loose, on the wrong part of the line, or exposed to ambient air reads inaccurately and drives the valve into oscillation. A dirty condenser raises head pressure steadily rather than causing rapid cycling of the valve. A restricted drier starves the valve continuously instead of making it swing. And worn compressor valves reduce capacity smoothly without producing a 30-second oscillation.

How does an electronic expansion valve differ from a thermostatic expansion valve?

• a.It uses sensors and a controller to position the valve electronically✓
• b.It maintains a fixed orifice area independent of load
• c.It regulates head pressure instead of evaporator superheat
• d.It requires no superheat measurement to operate

An electronic valve reads temperature and pressure sensors and drives a stepper motor, giving faster and more precise control over a wider range. It still controls superheat, so it very much depends on measuring it. A fixed area is the defining feature of an orifice or capillary, not an EEV. And head pressure control is a separate function performed by other devices.

A residential heat pump's accumulator serves what function?

• a.Holding liquid on the suction side and metering oil back gradually✓
• b.Separating oil from refrigerant leaving the compressor
• c.Reducing the pressure of vapor entering the compressor
• d.Storing excess liquid refrigerant on the high side of the system loop

A suction accumulator catches liquid that returns from the coil, especially at defrost changeover, and feeds oil and refrigerant back to the compressor at a controlled rate. High-side liquid storage is the job of a receiver. Oil separation at the discharge is done by an oil separator. And nothing in an accumulator is designed to reduce suction pressure.

During heat pump defrost, what happens inside the system?

• a.The outdoor fan speeds up to blow frost off the coil
• b.The reversing valve shifts to cooling and the outdoor fan stops✓
• c.The reversing valve holds position while the metering device reverses
• d.Auxiliary heat is energized while the compressor stops

In a reverse-cycle defrost the valve shifts so hot discharge gas flows to the outdoor coil, and the outdoor fan is stopped so that heat melts the frost rather than being blown away. Speeding the fan would only cool the coil further. The compressor keeps running because it is the source of the defrost heat, though auxiliary heat may be added to temper indoor air. And it is the reversing valve, not the metering device, that changes the flow direction.

A demand-defrost control differs from a time-and-temperature control in what way?

• a.It eliminates the need for a defrost termination sensor
• b.It defrosts using electric heaters instead of reversing the cycle
• c.It runs a defrost cycle at every compressor start in winter
• d.It initiates defrost based on measured coil conditions rather than a fixed clock✓

Demand defrost compares coil and ambient temperatures or airflow indicators and defrosts only when frost has actually accumulated, saving energy and run time. Reverse-cycle defrost is used by both control types on residential heat pumps. Defrosting at every start would waste more energy than the timer approach it replaces. And a termination sensor is still needed to end the cycle when the coil is clear.

What does the compression ratio of a refrigeration system describe?

• a.Mass flow at the discharge divided by the mass flow at the suction
• b.Gauge discharge pressure divided by gauge suction pressure
• c.The volume of the cylinder divided by its clearance volume
• d.Absolute discharge pressure divided by absolute suction pressure✓

Compression ratio uses absolute pressures, so atmospheric pressure must be added to both gauge readings before dividing. Cylinder volume over clearance volume describes a mechanical design property, not the operating ratio. Using gauge pressures gives a number that changes meaning with altitude and is not the standard definition. And mass flow is identical at both points in a sealed steady-state system.

Why does a rising compression ratio reduce a compressor's capacity?

• a.Gas trapped in the clearance volume re-expands, reducing the vapor drawn in✓
• b.The motor loses torque as discharge pressure increases
• c.The metering device closes to protect against high pressure
• d.The refrigerant's latent heat of vaporization falls sharply as pressure rises

High-pressure gas left in the clearance space expands on the down stroke and occupies part of the cylinder, so less new vapor enters and volumetric efficiency drops. Motor torque follows the load rather than collapsing as pressure rises. Metering devices respond to superheat or pressure drop, not to protecting the compressor. And while latent heat does change with pressure, the volumetric efficiency loss is the dominant effect.

A scroll compressor is being replaced. Which characteristic distinguishes it from a reciprocating compressor?

• a.It compresses continuously with two mating spiral elements✓
• b.It tolerates a continuous liquid return without internal damage
• c.It requires no crankcase heater under any condition
• d.It can be operated in either rotational direction

A scroll uses an orbiting spiral against a fixed spiral, giving smooth continuous compression with few moving parts. It tolerates brief liquid slugs better than a reciprocating machine but is still damaged by continuous flooding. Three-phase scrolls are direction sensitive and will not pump if phased backwards. And crankcase heaters are still applied to scrolls in cold ambient applications.

What is the practical difference between liquid slugging and flooding in a compressor?

• a.Slugging occurs only at startup; flooding occurs only at shutdown
• b.Slugging is caused by low charge; flooding is caused by high superheat
• c.Slugging is a sudden incompressible charge of liquid; flooding is gradual liquid return diluting oil✓
• d.Slugging affects scroll compressors; flooding affects reciprocating compressors

Slugging is a mechanical event in which liquid enters the compression chamber and cannot be compressed, while flooding is the slower washing of oil from bearings by returning liquid. Both can occur at startup or in steady operation depending on the cause. Both failure modes occur in either compressor type. And low charge and high superheat produce overheating, which is the opposite of a liquid-related failure.

Polyolester oil is used with modern refrigerants. What handling precaution does it require?

• a.It cannot be used in systems that contain a liquid line filter drier
• b.It must be blended with mineral oil before use
• c.It must be stored below freezing to prevent separation
• d.It absorbs moisture rapidly, so containers stay sealed until use✓

Polyolester oil is hygroscopic and pulls water from room air within minutes, and that moisture forms acids in the system. Blending it with mineral oil defeats the miscibility it was chosen for. Refrigeration oils are stored at normal temperatures, and freezing is not a requirement. And a filter drier is exactly what these systems need to control the moisture the oil attracts.

Non-condensable gases have entered a system. What symptom is most characteristic?

• a.Suction pressure far below normal with high superheat
• b.Low head pressure with normal subcooling
• c.Head pressure higher than the condensing temperature would predict✓
• d.Compressor amperage well below rated load amps

Air occupies condenser volume and adds its own partial pressure, so head pressure reads high relative to the temperature the liquid line actually shows. Low suction with high superheat is a starvation symptom from restriction or undercharge. Low head pressure would mean the condenser is rejecting heat too easily, the opposite condition. And amperage rises rather than falls when head pressure is elevated.

How does moisture in a refrigerant circuit cause damage?

• a.It reacts with refrigerant and oil to form acids and can freeze at the metering device✓
• b.It coats the condenser tubes and blocks heat transfer
• c.It reacts with copper to plate the compressor bearings
• d.It raises the refrigerant's boiling point in the evaporator

Water combines with refrigerant and oil to produce acids that attack windings, and free water can freeze at the expansion device and block flow. Boiling point in the evaporator is set by pressure, not by trace moisture. Moisture stays in circulation rather than coating condenser tubes. And copper plating is a real failure but is a secondary effect of acid formation, not the direct mechanism of moisture damage.

What does a liquid line filter drier with a high pressure drop across it indicate?

• a.The compressor is producing excess discharge pressure
• b.The drier was installed with the arrow pointing correctly
• c.It is loaded with debris and is restricting refrigerant flow✓
• d.The system is overcharged and liquid is stacking behind the drier

A significant temperature or pressure drop across the drier means the media is plugged and is starving the metering device. Overcharge raises pressure throughout the high side without creating a localized drop across one component. Excess discharge pressure would show up at the compressor, not as a drop across the drier. And correct installation direction is a good thing, not something a pressure drop reveals.

Which EPA Section 608 certification type covers residential split-system air conditioners containing more than five pounds of refrigerant?

• a.Type I
• b.Type II✓
• c.Type III
• d.Apprentice

Type II certification covers high-pressure and very high-pressure appliances, which includes residential and commercial split systems and heat pumps. Type I is limited to small appliances charged with five pounds or less at the factory. Type III covers low-pressure chillers that operate below atmospheric pressure. And there is no apprentice category in the Section 608 certification scheme.40 CFR Part 82, Subpart F (EPA Section 608)

What is the difference between recovering and reclaiming refrigerant?

• a.Recovery restores refrigerant to new purity; reclamation only removes it
• b.Recovery requires certification; reclamation does not
• c.Recovery applies only to blended refrigerants; reclamation applies only to single-component ones
• d.Recovery removes refrigerant from the system; reclamation reprocesses it to a purity standard✓

Recovery simply means removing refrigerant into a container, while reclamation means processing it, usually off site, to meet a recognized purity specification. Certification is required to handle regulated refrigerant either way. The purity restoration definition belongs to reclamation, not recovery. And both processes apply regardless of whether the refrigerant is a blend or a single compound.40 CFR Part 82, Subpart F (EPA Section 608)

A technician plans to recycle refrigerant on site with a recovery and recycling machine. What does recycling accomplish?

• a.It cleans refrigerant by separating oil and passing it through filters and driers✓
• b.It certifies that the refrigerant now meets the published reclamation purity standard
• c.It converts one refrigerant into another compatible blend
• d.It removes all non-condensable gases and water to laboratory levels

On-site recycling reduces contaminants through oil separation and filtration or drying, and the refrigerant is returned to equipment typically owned by the same customer. Meeting a purity standard requires laboratory reclamation, which a field machine cannot certify. No field process converts one refrigerant into another. And a recycling machine reduces but does not eliminate moisture and non-condensables to laboratory levels.40 CFR Part 82, Subpart F (EPA Section 608)

A recovery cylinder is being filled. What fill limit applies?

• a.95 percent of the cylinder's rated capacity by weight
• b.80 percent of the cylinder's internal volume by sight
• c.100 percent as long as the cylinder is kept below 90 F
• d.80 percent of the cylinder's rated capacity by weight✓

Recovery cylinders are filled to no more than 80 percent by weight so liquid can expand without hydrostatically rupturing the cylinder. Judging volume by sight is not possible in an opaque steel cylinder and is not the standard. Filling to 95 percent leaves too little vapor space for thermal expansion. And keeping a full cylinder cool is not a substitute for the fill limit, since ambient conditions change in a truck.40 CFR Part 82, Subpart F (EPA Section 608)

Which practice is prohibited under EPA Section 608 when servicing an air conditioner?

• a.Recovering refrigerant into a certified recovery cylinder
• b.Using nitrogen to pressure test a repaired refrigerant circuit
• c.Knowingly releasing refrigerant to the atmosphere during service or disposal✓
• d.Adding refrigerant to a system that has a known small leak after the repair is made

Knowingly venting a regulated refrigerant during maintenance, service, repair, or disposal is the core prohibition of the rule. Recovering into a certified cylinder is exactly what the rule requires. Recharging after a leak is repaired and verified is permitted. And nitrogen pressure testing is a standard, allowed procedure that produces no refrigerant emission.40 CFR Part 82, Subpart F (EPA Section 608)

R-410A and R-454B are being compared for a residential change-out. Which statement reflects a real operating difference?

• a.R-454B operates at roughly twice the pressure of R-410A
• b.R-410A requires mineral oil while R-454B requires polyolester oil
• c.R-454B is classified A2L, so listed equipment includes mitigation features✓
• d.R-410A can be safely charged as vapor because it behaves as a single compound

R-454B carries an A2L safety classification for mild flammability, and equipment designed for it includes charge limits, sensors, or other listed mitigation. Their operating pressures are broadly similar, not double. Both use polyolester-type synthetic oils rather than mineral oil. And R-410A is a near-azeotropic blend that is still charged as liquid, not a single compound.

What does temperature glide mean for a zeotropic refrigerant blend?

• a.Saturation temperature changes across the coil at constant pressure✓
• b.The refrigerant loses capacity gradually as the system ages
• c.The blend separates permanently once it enters the evaporator
• d.The refrigerant's pressure changes while its temperature stays fixed

In a zeotropic blend the components boil at different temperatures, so saturation temperature rises through the evaporator even though pressure is nearly constant, and the technician must use the correct dew or bubble point value. Pressure changing at fixed temperature describes a different process entirely. Capacity loss over time is a maintenance issue, not a property of the blend. And the components mix again in the vapor phase rather than separating permanently.

Why must a zeotropic blend be charged into a system as liquid rather than vapor?

• a.Liquid charging is the only way to weigh the charge accurately
• b.Vapor charging removes the lighter component first and changes the blend✓
• c.Liquid charging is required to lubricate the compressor bearings
• d.Vapor charging cannot reach the pressure needed to fill the entire system

The components of a blend have different vapor pressures, so drawing vapor from the cylinder pulls off the most volatile component and leaves a different mixture behind. Cylinder pressure is adequate for vapor transfer in many conditions, so pressure is not the barrier. Oil is charged separately and does not travel with the refrigerant from the cylinder. And a scale weighs the cylinder accurately regardless of which phase leaves it.

A technician needs the saturation temperature for a measured pressure on an A2L blend. Where does that number come from?

• a.The rule that saturation temperature is 35 degrees below ambient
• b.The equipment nameplate's design pressure rating
• c.The pressure-temperature data published for that specific refrigerant✓
• d.The generic pressure-temperature scale printed on the manifold gauge face

Each refrigerant has its own pressure-temperature relationship, and blends additionally have separate bubble and dew point columns, so the specific published data must be used. A generic gauge scale covers only the few refrigerants printed on it. Nameplate design pressure is a structural limit, not an operating relationship. And there is no valid rule tying saturation temperature to a fixed offset from ambient.

What does latent heat of vaporization describe in the refrigeration cycle?

• a.The heat rejected as the vapor is desuperheated in the discharge line
• b.The heat stored in the compressor oil during normal operation
• c.The heat that raises the vapor's temperature after it leaves the coil
• d.The heat absorbed as refrigerant changes from liquid to vapor at constant temperature✓

Latent heat is the energy a refrigerant absorbs while boiling without changing temperature, and it is the mechanism that moves the bulk of the heat load. Heating vapor above its boiling point is sensible superheat, not latent heat. Desuperheating in the discharge line is also a sensible process. And oil is a lubricant, not a thermal storage medium in the cycle.

Two systems run at the same suction pressure, but one has 5 degrees of superheat and the other has 30. Which statement is accurate?

• a.The 5-degree system is at greater risk of compressor overheating
• b.Both systems must have the same evaporator capacity
• c.The 30-degree system is using more of its evaporator surface for boiling refrigerant
• d.The 30-degree system risks overheating; the 5-degree system risks liquid return✓

High superheat means the refrigerant boiled off early and the returning vapor is hot, while very low superheat means liquid may reach the compressor. High superheat wastes evaporator surface on sensible heating rather than using more of it for boiling. It is the high-superheat system, not the low one, that runs the compressor hot. And unequal superheat means unequal use of the coil, so capacity is not the same.

How does a compressor's discharge temperature respond to very high suction superheat?

• a.It stays constant, because the compression ratio governs it entirely
• b.It rises, because hotter suction gas enters the compression stroke✓
• c.It falls, because thinner vapor carries less heat
• d.It rises only if the condenser is also dirty

Return gas temperature is one of the two main inputs to discharge temperature, so hot suction vapor produces very hot discharge gas that can break down oil. Lower vapor density reduces mass flow but does not cool the discharge. Compression ratio matters but does not act alone. And the effect appears with a clean condenser as well, since it originates on the suction side.

A hermetic compressor motor is cooled by what in a typical residential system?

• a.The returning suction gas passing through the motor windings✓
• b.The outdoor fan blowing air over the compressor shell
• c.The liquid line passing back through the compressor housing wall
• d.The oil sump circulating through an external cooler

Suction-cooled hermetic compressors route return gas over the motor before compression, which is why chronically high superheat overheats the windings. Cabinet airflow provides some incidental cooling but is not the design cooling path. External oil coolers appear on large industrial machines, not residential hermetics. And the liquid line never passes through the compressor housing.

What is the primary function of a receiver in systems that have one?

• a.To separate oil from the discharge gas before the condenser
• b.To store liquid refrigerant so charge can vary with load✓
• c.To protect the compressor from returning liquid at startup
• d.To lower head pressure by adding condenser volume

A receiver holds a reservoir of liquid on the high side so the metering device always has liquid available as operating conditions change. Protecting the compressor from liquid on the suction side is the accumulator's job. Oil separation happens in an oil separator at the discharge. And a receiver does not add effective condensing surface, so it does not lower head pressure.

Head pressure control is applied to a system operating in cold outdoor conditions. Why is it needed?

• a.To prevent the compressor from overheating in low ambient
• b.To maintain enough pressure difference for the metering device to feed properly✓
• c.To keep the condenser fan running at full speed year round
• d.To prevent the suction line from freezing at the compressor

If head pressure falls too far, there is not enough pressure drop across the metering device to feed the evaporator, and the system starves. Compressor overheating is a high-superheat or high-compression-ratio problem, not a low ambient one. Head pressure control typically slows or cycles the condenser fan rather than keeping it at full speed. And the suction line does not freeze from low head pressure.

A capillary tube system reaches equilibrium during the off cycle. What does that mean for restarting?

• a.Pressures equalize, so the compressor can start against a low load✓
• b.Pressures stay split, requiring a hard start kit on every unit
• c.The metering device closes tightly to hold back the high side pressure
• d.The compressor must be started manually with a jumper

A capillary tube is an open restriction, so pressures equalize during the off cycle and the compressor faces a light starting load, which is why these systems often use lower-torque motors. Pressure does not stay split, because nothing closes the passage. Capillaries have no valve to close tightly. And no manual starting procedure is involved in normal operation.

An evaporator coil is icing over on an 80 F day with the system running continuously. What are the two most likely causes?

• a.Low airflow across the coil or a refrigerant undercharge✓
• b.High outdoor ambient or a dirty condenser coil
• c.Overcharge or a stuck-open reversing valve
• d.A failed crankcase heater or a loose thermostat anticipator

Icing means the coil is operating below freezing, which follows from too little heat reaching it or too little refrigerant boiling in it, so restricted airflow and low charge lead the list. Overcharge raises suction pressure and works against icing. A dirty condenser raises head pressure without dropping the coil below freezing. And crankcase or thermostat problems affect starting and cycling, not coil temperature.

How does an undercharged system produce a frozen evaporator?

• a.The condenser cannot reject heat, so the coil temperature drops
• b.Suction pressure falls until the saturation temperature is below freezing✓
• c.The metering device opens wider and floods the coil with cold liquid
• d.The compressor runs hotter and transfers some of that heat back to the coil

With too little refrigerant, suction pressure drops and the corresponding saturation temperature falls below 32 F, so condensate freezes on the fins. Compressor heat travels with the discharge gas toward the condenser, not backward into the evaporator. A condenser that cannot reject heat raises pressures throughout, which does not freeze a coil. And flooding the coil would raise suction pressure and coil temperature.

A technician finds a system that is overcharged. Which set of readings fits that condition on a TXV system?

• a.Low head pressure, low subcooling, and high superheat
• b.High head pressure, high subcooling, normal superheat✓
• c.High head pressure, low subcooling, and high superheat
• d.Low head pressure, high subcooling, and normal superheat

Extra refrigerant stacks in the condenser, so subcooling and head pressure both climb while the TXV keeps superheat near its setting. Low head pressure with low subcooling describes an undercharge. High head with low subcooling suggests non-condensables or a condenser problem instead. And high subcooling with low head pressure is an inconsistent combination on an operating system.

What is the purpose of a low-pressure control on a residential split system?

• a.To reverse the compressor when the coil begins to frost
• b.To stop the compressor when suction pressure indicates loss of charge✓
• c.To modulate the metering device as load changes
• d.To keep the evaporator from ever operating above its design pressure limit

A low-pressure switch opens when suction pressure falls below its setpoint, protecting the compressor from running with insufficient refrigerant. Preventing high pressure is the high-pressure control's role. Metering devices modulate on their own control inputs, not from a pressure switch. And no residential control reverses a compressor's rotation in response to frost.

A refrigerant leak is suspected in an attic coil. Which detection method is best suited to pinpointing it?

• a.Adding a can of sealant and monitoring pressures afterward
• b.Watching for an oil stain on the drain pan over the next several weeks
• c.Comparing the suction pressure before and after the coil
• d.An electronic leak detector swept slowly along the tubing and returns✓

A heated diode or infrared detector moved slowly along joints and return bends locates the leak precisely and is the standard field method. Oil staining is a useful clue but is slow and often absent on small leaks. Pressure drop across a coil reflects flow restriction, not leakage. And sealants can plug metering devices and driers and do not identify where the leak is.

A large leak has emptied a system. What must be done before the system is recharged?

• a.Install a larger metering device to restore capacity
• b.Add extra refrigerant to compensate for the loss
• c.Run the compressor briefly to circulate any oil left in the lines
• d.Repair the leak, then pressure test, evacuate, and verify✓

The leak has to be found and repaired, the repair proven with a pressure test, and the system evacuated to remove air and moisture that entered before the charge goes in. Simply adding refrigerant releases it again and is prohibited. Running a compressor with no charge damages it and does nothing useful. And changing the metering device does not address the loss of refrigerant or the entry of contaminants.

A compressor has burned out and the oil smells acidic. What service step protects the replacement compressor?

• a.Cleaning the system and installing a suction line filter drier and a new liquid line drier✓
• b.Installing a sight glass in the liquid line to monitor moisture
• c.Charging the system with 10 percent extra refrigerant
• d.Reusing the original filter drier after blowing it out with nitrogen

A burnout leaves acid and debris throughout the circuit, so the system is cleaned and both a suction line filter and a fresh liquid line drier are installed to capture what remains. Overcharging changes operating conditions and removes nothing. A moisture-indicating sight glass reports a condition but does not clean the system. And a used drier is already saturated and cannot be restored by blowing it out.

Which condition explains high suction pressure together with low head pressure on a cooling system?

• a.Worn compressor valves or an internal bypass in the compressor✓
• b.A dirty outdoor condenser coil
• c.A plugged liquid line filter drier
• d.An oversized metering device installed on an otherwise correct system

A compressor that is no longer pumping lets the two sides drift toward each other, raising suction while head pressure falls. A plugged drier starves the low side and drops suction pressure instead. A dirty condenser raises head pressure. And an oversized metering device floods the evaporator, raising suction pressure but not lowering head pressure.

How is a compressor's pumping ability verified in the field?

• a.By measuring the resistance of the run and the start windings when cold
• b.By measuring the voltage drop across the contactor
• c.By closing the suction service valve and observing how low it pulls✓
• d.By comparing the amp draw to the locked rotor amps

A closed-valve pump-down test shows whether the compressor can pull and hold a low suction pressure, which directly measures pumping capability. Winding resistance is an electrical check that says nothing about mechanical pumping. Contactor voltage drop tests the contact, not the compressor. And locked rotor amps is a starting characteristic, not a pumping measurement.

A heat pump in heating mode has the reversing valve stuck in the cooling position. What will the customer report?

• a.The system heats but never satisfies on the coldest days
• b.The outdoor unit runs but the indoor blower never starts
• c.The system heats normally but the defrost cycle never runs
• d.Cold air comes from the registers on a call for heat✓

If the valve does not shift, the indoor coil keeps acting as an evaporator and the registers deliver cold air while the thermostat calls for heat. Falling short on the coldest days is the normal behavior of a heat pump near its balance point. A blower that never starts is a control or motor fault. And a heat pump that heats normally is by definition shifting the valve correctly.

Which measurement best confirms that an outdoor condenser coil is rejecting heat properly?

• a.Static pressure across the outdoor coil
• b.Condensing temperature compared with the outdoor ambient✓
• c.Suction line temperature measured at the compressor inlet
• d.Amperage of the outdoor fan motor

A healthy air-cooled condenser condenses at a predictable margin above the entering air temperature, so comparing the two reveals fouling or airflow loss. Suction line temperature reflects evaporator and line conditions. Fan amperage indicates the motor is turning but not that the coil is clean. And static pressure is not a practical measurement across an open outdoor coil.

Why does a dirty evaporator coil reduce capacity even though the refrigerant charge is correct?

• a.It insulates the tubing, so the refrigerant leaves the coil as liquid
• b.It raises head pressure, which reduces compressor displacement
• c.It causes the metering device to overfeed and flood the compressor
• d.It restricts airflow, so less heat reaches the refrigerant and suction pressure falls✓

A blocked coil starves the refrigerant of heat, so boiling slows, suction pressure and coil temperature drop, and capacity falls. The refrigerant leaving a starved coil is heavily superheated vapor, not liquid. Head pressure actually tends to fall because less heat is being absorbed and moved. And a starved coil makes the metering device throttle back rather than overfeed.

What does the coefficient of performance describe for a heat pump?

• a.The percentage of input fuel converted to usable heat
• b.The ratio of heat output to energy input in consistent units✓
• c.The ratio of BTU output to watts input measured at rated conditions
• d.The seasonal average of heating output over a full winter

COP is a unitless ratio of energy delivered to energy consumed, and it can exceed 1.0 because a heat pump moves heat instead of creating it. Fuel conversion percentage describes combustion efficiency and cannot exceed 100 percent. A seasonal average across a heating season is HSPF, a different metric. And BTU per watt is the definition of EER, which mixes units rather than being unitless.

A service valve core is removed to speed evacuation. What is the risk if it is not reinstalled?

• a.The system will read a false high suction pressure
• b.The gauge hose cannot be attached to the port again
• c.The compressor will not build head pressure at startup
• d.The cap alone is the remaining seal, and refrigerant can leak past it✓

The valve core is the primary seal at a service port, and a cap is only a secondary seal, so an omitted core will leak the charge over time. Hoses attach to the port fitting whether or not a core is present. Suction pressure readings are unaffected by the core's presence. And nothing about a missing core prevents the compressor from building pressure.

Which practice reduces refrigerant loss every time gauges are connected and removed?

• a.Connecting only the low-side hose on every service call
• b.Leaving the hoses attached between visits to the same customer site
• c.Using low-loss hose fittings and recovering what the hoses hold✓
• d.Purging the hoses with refrigerant before connecting them

Low-loss fittings close the hose ends, and recovering the hose contents keeps the trapped charge out of the atmosphere. Using one hose does not eliminate the loss from that hose. Leaving hoses attached exposes them to weather and does not prevent loss at removal. And purging hoses with refrigerant deliberately vents it, which is exactly what the rules prohibit.

What happens to the pressure in a refrigerant cylinder as its temperature rises?

• a.It changes only if the cylinder is more than half full
• b.It falls, because the vapor expands into the free space
• c.It rises, following the refrigerant's saturation curve✓
• d.It stays constant as long as liquid remains in the cylinder

A cylinder holding both liquid and vapor sits on the saturation curve, so warming it raises pressure steadily, which is why cylinders must be protected from heat. Constant pressure would require constant temperature, not merely the presence of liquid. Vapor expanding in a sealed container raises pressure rather than lowering it. And the relationship holds at any fill level, though a fuller cylinder is more dangerous because liquid expands.

A technician wants to recover refrigerant quickly from a system with a large charge. What technique speeds it up?

• a.Warming the recovery cylinder in order to raise its internal pressure
• b.Running the system's own compressor during the recovery
• c.Recovering liquid first through both service ports with short hoses✓
• d.Connecting the recovery machine only to the suction port

Pulling liquid through both ports with short, large-diameter hoses moves the bulk of the charge fast, and the remaining vapor is recovered afterward. Warming the recovery cylinder raises the pressure the machine must push against and slows it. Running the system compressor during recovery risks damaging it and is not the intended method. And a single suction connection forces slow vapor-phase recovery of the whole charge.

During a pump-down for a component replacement, what is the goal?

• a.To equalize pressures so the compressor can restart under no load
• b.To isolate the charge in the condenser and receiver so the low side can be opened✓
• c.To lower the system to a deep vacuum before opening it
• d.To transfer the charge into the recovery cylinder for disposal

Pumping down uses the system's own compressor to store refrigerant behind a closed service valve so low-side work can be done without recovering the entire charge. A deep vacuum requires a vacuum pump and comes after the system is opened and repaired. Transferring to a cylinder is recovery, a separate procedure. And equalizing pressures is a starting consideration, not the purpose of a pump-down.

What determines the evaporator's saturation temperature during normal operation?

• a.The thermostat setpoint selected by the occupant
• b.The superheat setting adjusted at the expansion valve
• c.The suction pressure the compressor and metering device establish✓
• d.The outdoor ambient temperature at the condenser

Saturation temperature is fixed by pressure, and the balance between compressor pumping and metering device feed sets the suction pressure in the coil. The thermostat decides when the system runs, not the pressure inside it. The superheat adjustment shifts how much of the coil boils but does not set the saturation point itself. And outdoor ambient controls the high side rather than the evaporator's pressure.

A condenser hums but the fan and compressor do not start, and both begin running after you spin the fan blade by hand. What component should you test first?

• a.The dual run capacitor✓
• b.The contactor coil
• c.The low-pressure switch
• d.The compressor windings

A motor that hums and then runs after a manual push has lost its phase shift, which points straight at the run capacitor. The contactor is clearly pulling in, since power is reaching the motors. A tripped low-pressure switch would leave the unit silent rather than humming. And the compressor windings are proven by the fact that it eventually runs.

A dual run capacitor is marked 45/5 microfarads. What does the smaller value serve?

• a.The defrost board's timing circuit
• b.The compressor start winding during the first second of operation
• c.The low-voltage transformer's secondary circuit
• d.The condenser fan motor✓

On a dual capacitor the large value serves the compressor and the small value serves the condenser fan motor, with a common terminal shared between them. Start assistance for the compressor comes from a separate start capacitor and potential relay when one is used. The control transformer is not capacitor driven. And defrost timing is handled electronically on the board, not by a run capacitor.

You measure a 45 microfarad capacitor at 31 microfarads. What is the correct action?

• a.Replace it, because it is well outside its tolerance✓
• b.Wait until the compressor fails to start before replacing it
• c.Add a second capacitor in series to make up the difference
• d.Leave it, because any reading above 30 is acceptable

Run capacitors carry a tolerance of a few percent, and a 31 microfarad reading on a 45 microfarad part means the motor is running with reduced torque and elevated current. There is no rule accepting anything above 30. Capacitors in series reduce total capacitance rather than increasing it. And waiting for a hard-start failure lets the weak capacitor overheat the windings in the meantime.

What must be done to a capacitor before it is tested or handled?

• a.Note the polarity marking on the case
• b.Verify the microfarad rating with the manufacturer
• c.Warm it to room temperature so that the reading is accurate
• d.Discharge it safely across a resistor with power removed✓

A capacitor holds a charge after power is off, so it must be discharged through a resistor before it is touched or tested. Temperature has little effect on a field capacitance reading. Motor run capacitors are non-polarized, so there is no polarity marking to observe. And confirming the rating with the manufacturer is a parts question, not a safety step.

A contactor's contacts are visibly pitted and the compressor chatters at startup. What is the risk of leaving it in service?

• a.Voltage drop and arcing across the contacts can damage the compressor✓
• b.The condenser fan will run backwards
• c.The low-voltage transformer will be overloaded
• d.The capacitor will discharge through the contacts

Pitted contacts add resistance and cause voltage drop and repeated arcing, which subject the compressor to low-voltage starting and heat. The transformer supplies only the small coil current and is not overloaded by contact condition. Capacitors discharge through motor windings, not through line contacts. And single-phase fan rotation is fixed by the motor's internal wiring.

A 24-volt control transformer is replaced twice and burns out both times. What should you investigate?

• a.A shorted control wire or a failed contactor coil drawing excess current✓
• b.A refrigerant overcharge raising compressor amperage
• c.A thermostat mounted on an exterior wall
• d.An oversized filter causing high static pressure

Repeat transformer failures come from an overloaded secondary, which usually means a pinched or shorted thermostat wire or a coil that has shorted turns. Airflow restriction and refrigerant charge act on the line-voltage side and do not load the control transformer. And a poorly located thermostat causes comfort complaints and short cycling, not transformer burnout.

The correct sequence of operation for a modern gas furnace begins with which event after the thermostat calls?

• a.The main blower starts at heating speed
• b.The inducer starts and proves the pressure switch✓
• c.The gas valve opens to purge the manifold
• d.The hot surface igniter warms while the blower runs

The control energizes the inducer first and waits for the pressure switch to close, proving that the venting path is open before ignition can proceed. Opening the gas valve before proving draft would release unburned gas. Heating the igniter comes after the pressure switch proves. And the main blower starts on a timed delay after flame is established.

A furnace inducer runs but the pressure switch never closes. Which cause should be checked first?

• a.A cracked hot surface igniter
• b.A dirty flame sensor coated with oxide
• c.A weak thermostat battery reducing the call voltage below spec
• d.A blocked vent, plugged drain, or disconnected sensing hose✓

The pressure switch proves the inducer is actually moving flue gas, so blockages in the vent, the condensate trap, or the sensing hose are the usual causes. A cracked igniter fails later in the sequence, after the switch closes. A weak thermostat battery would prevent the call from being made at all. And a dirty flame sensor causes a lockout after ignition, not a failure to prove draft.

How does a flame sensor prove the presence of flame on a modern furnace?

• a.It measures the temperature rise at the burner face
• b.It passes a small DC current through the flame by rectification✓
• c.It detects the pressure pulse ignition creates
• d.It measures the infrared light the flame emits

A flame rectification circuit sends alternating current through the flame, which conducts in only one direction, producing a microamp DC signal the board reads. Optical sensing is used on oil burners and some commercial equipment, not on this circuit. Thermocouples measure heat and are used on standing pilot systems. And no pressure pulse is used to prove flame.

A furnace lights, runs for about six seconds, then shuts down and retries. What is the most probable cause?

• a.A dirty or misaligned flame sensor✓
• b.A failed inducer motor bearing assembly
• c.An undersized gas supply line
• d.A cracked heat exchanger

Ignition followed by a short run and a retry is the classic signature of a flame sensing failure, since the board proves flame for a few seconds and then loses the signal. A failed inducer would stop the sequence before ignition. A cracked heat exchanger produces flame disturbance and rollout symptoms rather than a clean lockout pattern. And an undersized gas line usually shows as a weak or unstable flame at high fire, not a consistent short cycle.

A rollout switch on a gas furnace has tripped. What must the technician do?

• a.Find and correct the cause of flame escaping the burner box✓
• b.Reset it and monitor the furnace on the next several cycles
• c.Jumper it temporarily so the customer has heat overnight
• d.Replace it with a switch of a higher temperature rating

A rollout switch trips because flame left the combustion chamber, usually from a blocked flue, a plugged heat exchanger, or a cracked passage, and that cause must be corrected. Simply resetting it leaves a combustion hazard in service. Raising the trip temperature defeats the protection the switch provides. And jumpering a safety device on a fuel-burning appliance is never acceptable.

A furnace repeatedly trips its high-limit switch during heating. Which cause is most likely?

• a.A thermostat set too low for the occupant's comfort
• b.An oversized return duct delivering excess air
• c.Restricted airflow from a dirty filter, closed registers, or a failing blower✓
• d.A refrigerant undercharge in the cooling circuit

The high limit opens when heat exchanger temperature climbs, and the usual reason is that not enough air is carrying that heat away. The cooling circuit's charge has no role in a heating cycle. A low setpoint would shorten the run rather than overheat the exchanger. And too much return air would lower temperature rise, moving away from the limit rather than toward it.

A combustion analysis on a natural gas furnace shows 400 ppm of carbon monoxide air-free in the flue. How should the technician respond?

• a.Increase the manifold pressure to burn the gas more completely
• b.Record it as acceptable and complete the service call
• c.Open a nearby window and retest to dilute the reading
• d.Investigate the cause and correct the combustion problem✓

An air-free carbon monoxide reading in the hundreds of parts per million signals incomplete combustion from a dirty burner, restricted venting, or a cracked exchanger, and it must be diagnosed. Recording it as acceptable ignores a life-safety indicator. Raising manifold pressure typically overfires the burner and makes carbon monoxide worse. And ventilating the room changes the ambient reading without changing what the appliance produces.

What does a yellow, lazy flame on a natural gas burner most often indicate?

• a.A cracked hot surface igniter near the flame
• b.Insufficient primary air or a dirty burner✓
• c.Excess combustion air reaching the burner
• d.Gas pressure below the manifold rating

Yellow tipping and a lazy flame show incomplete mixing of gas and primary air, usually from lint, rust, or a blocked burner port. Excess air produces a lifting, noisy blue flame rather than a yellow one. Low gas pressure gives a small, weak flame that is still blue. And a cracked igniter fails to light the burner instead of changing flame color.

A hot surface igniter glows but the burner never lights. What should be checked next?

• a.The condensate float switch
• b.The evaporator coil for ice
• c.The blower motor capacitor
• d.Gas supply and the gas valve's operation✓

If the igniter reaches temperature and no flame appears, the missing element is fuel, so the gas supply, shutoff position, and valve operation are the next checks. Blower components affect air movement after ignition. A tripped float switch would interrupt the call before the igniter energized. And evaporator ice belongs to the cooling side and has no role in the ignition sequence.

A technician measures 0.95 in. w.c. of total external static on a system whose blower table is built around 0.50 in. w.c. What is the most productive next measurement?

• a.Line voltage at the disconnect
• b.Compressor amperage under load
• c.Superheat at the evaporator outlet
• d.Pressure drops across the filter, coil, and each duct section✓

Once total external static is known to be high, breaking it into component drops locates the restriction so the right thing gets fixed. Compressor amperage reflects refrigerant load and reveals nothing about which duct component is restrictive. Line voltage is an electrical supply check. And superheat is a refrigerant-side reading that will be distorted by the airflow problem rather than explaining it.

Which instrument gives the most direct measurement of the air a supply register is actually delivering?

• a.An infrared thermometer aimed at the grille face
• b.A digital manometer at the supply plenum
• c.An anemometer held in the center of the duct
• d.A powered flow hood placed over the register✓

A flow hood captures the entire discharge and reports CFM at that outlet directly. A single anemometer reading in the middle of a duct gives a velocity at one point, which must be traversed and converted. A manometer measures pressure, not volume. And an infrared thermometer reads surface temperature, which says nothing about airflow.

A blower wheel is caked with dust. What happens to airflow?

• a.It falls, because the dirty blades no longer grip and move air✓
• b.It stays the same because the motor compensates automatically
• c.It increases because the wheel is heavier and carries more momentum
• d.It falls only on ECM motors, not on PSC motors

Dirt fills the space between the blades so each pocket carries less air, and delivered CFM drops sharply even though the wheel still spins. Added mass does not push more air. A PSC motor holds speed but cannot recover the lost airflow, and an ECM raises torque and may partially compensate while drawing more watts. So the loss occurs with either motor type, not just one.

What advantage does a constant-airflow ECM blower have when duct static pressure is high?

• a.It shuts down and signals a fault on the control board
• b.It maintains a constant wattage regardless of resistance
• c.It reduces its speed to protect the motor from overload
• d.It increases speed and torque to hold the commanded CFM✓

A constant-airflow ECM senses torque and speed and ramps up to keep delivering the target CFM, though it consumes more watts doing it. It does not back off in response to static, which is the PSC behavior. Faulting out on high static is not how these motors respond within their range. And wattage rises rather than staying constant when the motor works harder.

Why can an ECM blower mask a duct problem from the homeowner while still costing them money?

• a.It holds airflow up by drawing more power, hiding the restriction✓
• b.It shifts the load to the compressor instead of the blower
• c.It quietly lowers airflow while still reporting normal operation to the board
• d.It defers the problem to the defrost board's fault log

Because the motor compensates for restriction, comfort stays acceptable while the electrical consumption climbs, so the defect shows up on the utility bill rather than as a complaint. It does not quietly reduce airflow; holding airflow is precisely what it does. Blower work is not transferred to the compressor. And a defrost board logs heat pump defrost events, not duct static problems.

A compressor draws locked rotor amps for a few seconds and then trips on overload repeatedly. What should be checked?

• a.The thermostat's heat anticipator setting
• b.The evaporator coil for a dirty filter media
• c.The condensate drain trap for standing water
• d.The start components, supply voltage, and whether pressures are equalized✓

A compressor stuck at locked rotor current is failing to start, so start capacitor and relay condition, supply voltage under load, and whether the system pressures have equalized are the diagnostic path. A condensate trap has nothing to do with starting torque. Anticipator settings affect cycle length in older thermostats. And a dirty filter reduces airflow without preventing the compressor from starting.

What does a hard start kit do for a struggling single-phase compressor?

• a.It lowers the voltage the compressor sees during startup
• b.It bypasses the run capacitor entirely while the motor is accelerating
• c.It delays the compressor start until head pressure builds
• d.It adds start winding current briefly to increase starting torque✓

A start capacitor and relay put extra current through the start winding for the first fraction of a second, boosting torque, and then drop out. It does not reduce supply voltage, which would make starting worse. The run capacitor stays in the circuit throughout. And a hard start kit does not create a timed delay; that is a separate anti-short-cycle control.

A compressor's common-to-ground resistance reads near zero ohms. What does that mean?

• a.The start winding has a higher resistance than normal
• b.The compressor is normal, since windings connect to the shell
• c.The motor windings are shorted to the shell and the compressor is failed✓
• d.The run winding is open and must be jumpered

Windings must be electrically isolated from the shell, so continuity to ground means the insulation has failed and the compressor is scrap. An open run winding would read infinite resistance between terminals, not to ground. Start winding resistance is measured terminal to terminal, not to the shell. And a healthy compressor reads very high resistance from any terminal to ground.

A heat pump runs constantly on a 35 F morning with the auxiliary heat energized the whole time. What should the technician verify first?

• a.Whether the low-pressure switch has been bypassed
• b.Whether the outdoor coil is frosted and the defrost control is working✓
• c.Whether the condensate float switch has tripped
• d.Whether the supply registers are set to the summer position

At that temperature a frosted outdoor coil that is not being defrosted destroys capacity and forces auxiliary heat to carry the load. A tripped float switch would stop the equipment rather than leave it running. Register position affects distribution but not the outdoor coil's condition. And a bypassed low-pressure switch is a wiring defect that would not by itself cause continuous auxiliary operation.

A customer reports the heat pump blows lukewarm air compared with their old furnace. What is the correct explanation?

• a.The auxiliary heat strips have failed open at the sequencer
• b.The system is undercharged and needs refrigerant added
• c.Heat pumps normally deliver a lower supply temperature over longer run times✓
• d.The reversing valve is leaking internally and must be replaced

A heat pump typically supplies air in the 90 to 105 degree range, which feels cool against skin but heats the house through longer run times. Adding refrigerant to a correctly charged system creates a different problem. An internally leaking reversing valve would show as poor capacity with an abnormally warm suction line, not as normal operation. And failed strips would matter only when supplemental heat was actually required.

A condensate float switch keeps interrupting the cooling call on an attic air handler. What is the correct repair?

• a.Wire the switch to the alarm circuit instead of the control circuit
• b.Clear the blockage in the drain and verify the trap and slope✓
• c.Remove the switch since a secondary pan is already installed
• d.Replace the switch with one rated for a higher water level

The switch is doing its job, so the drain restriction that is letting water rise must be found and cleared. Changing the trip level lets water climb closer to the ceiling before anything happens. Moving it to an alarm circuit removes the shutoff protection entirely. And a secondary pan is not a substitute for the shutoff device where one is required.

A cooling system shows low suction pressure, high superheat, and a frosted liquid line just past the filter drier. What is the diagnosis?

• a.A restriction at the drier causing a pressure drop and local cooling✓
• b.A blower running at too high a speed
• c.A reversing valve leaking internally
• d.An overcharge of refrigerant in the condenser

Frost appearing right after a component on the liquid line means refrigerant is flashing there, which is the signature of a restriction starving the evaporator. An overcharge raises suction pressure and subcooling instead. Excess blower speed raises suction pressure and lowers superheat. And a leaking reversing valve produces a warm suction line and poor capacity without a localized liquid line frost line.

How can a technician distinguish low airflow from low refrigerant charge when both produce low suction pressure?

• a.Low airflow shows a large temperature split; low charge shows high superheat with low subcooling✓
• b.Low airflow shows high head pressure; low charge shows high head pressure as well
• c.Low airflow trips the low-pressure switch; low charge never does
• d.Low airflow shows a wet suction line; low charge shows a dry suction line

Restricted airflow leaves the coil overcooling the small amount of air passing through it, producing a wide split, while a shortage of refrigerant shows itself as high superheat with little or no subcooling. Head pressure falls in both cases rather than rising in one. Suction line sweating depends on humidity and superheat and does not separate the two. And a severe airflow restriction can also drop suction low enough to trip the switch.

A system's head pressure is high and subcooling is high on a 90 F day with a clean condenser. What is the most likely cause?

• a.An overcharge of refrigerant✓
• b.A weak compressor with worn valves
• c.Low indoor airflow across the evaporator
• d.A restricted liquid line filter drier

Excess refrigerant stacks liquid in the condenser, which raises both subcooling and head pressure even when the coil and air are clean. A restricted drier would raise subcooling but starve the low side and lower head pressure. Low indoor airflow drops suction and head pressure together. And a weak compressor lowers head pressure while raising suction.

A customer's system cools well at night but struggles every afternoon. Which check addresses the pattern directly?

• a.Verify the thermostat's programmed schedule
• b.Check the condensate drain for a partial blockage
• c.Measure winding resistance on the compressor
• d.Measure condensing temperature against outdoor ambient at peak load✓

A complaint that tracks outdoor temperature points to heat rejection, so the condenser's approach temperature under peak conditions is the measurement that confirms or clears it. A thermostat schedule would produce the same behavior every day regardless of weather. Winding resistance is an electrical test unrelated to load. And drain condition affects water removal, not afternoon capacity.

What does SEER2 measure that EER does not?

• a.The electrical demand of the system at startup
• b.The efficiency of the ductwork attached to the system
• c.Seasonal performance across a range of conditions rather than one rating point✓
• d.The efficiency of the system in heating mode

SEER2 aggregates performance over a simulated cooling season, while EER reports efficiency at a single set of rating conditions. Heating efficiency is covered by HSPF2 and COP. Startup demand is a locked rotor characteristic, not an efficiency metric. And duct performance is measured separately by leakage testing, not by either rating.

Why were SEER2 and HSPF2 introduced to replace the earlier SEER and HSPF ratings?

• a.The ratings now include the cost of electricity in the region
• b.The ratings now cover only variable-speed equipment
• c.Testing moved from cooling season to heating season conditions
• d.Testing now uses a higher external static pressure closer to real installations✓

The revised test procedure raises the external static pressure used during testing so published numbers better reflect ducted systems in the field. The cooling and heating metrics still address their own seasons. Energy price is a local economic factor and is not part of any efficiency rating. And the ratings apply to single-stage equipment as well as variable-speed.

A homeowner asks whether a higher AFUE furnace will lower their bill in a mild coastal climate. What is the honest technical answer?

• a.AFUE only matters when the furnace is oversized for the load
• b.The savings depend on how many heating hours the house actually runs✓
• c.AFUE applies to the blower's electrical use rather than the fuel
• d.AFUE gains apply equally in every climate because efficiency is fixed

AFUE is a percentage of fuel converted to useful heat, so the dollar savings scale with how much fuel is burned across the season. The percentage is fixed, but the size of the savings is not, because it depends on run hours. Oversizing hurts efficiency in practice but does not determine whether AFUE matters. And AFUE addresses fuel conversion, while blower electricity is accounted separately.

A two-stage furnace never leaves low fire even on the coldest days. What should be checked?

• a.The staging control wiring and the second-stage thermostat call✓
• b.The condensate neutralizer for saturation
• c.The vent termination clearance from the wall
• d.The flame sensor microamp reading

Second-stage operation depends on a thermostat that can call for it and control wiring that carries the call, so those are the first things to verify. A saturated neutralizer affects drainage, not staging. The flame sensor proves flame at either stage and does not select one. And vent termination clearance is an installation dimension unrelated to staging logic.

An air conditioner short cycles, running four minutes and stopping for three all afternoon. Which cause fits best?

• a.The condensate trap has lost its water seal
• b.The blower motor is failing intermittently on its start winding
• c.The equipment is significantly oversized for the load✓
• d.The supply registers are open too far

Rapid on-off cycling under a steady load is the classic behavior of equipment with far more capacity than the house needs. A failing blower would produce airflow and overload symptoms rather than clean short cycles. A dry trap causes drainage and air-leakage problems, not cycling. And registers that are open too far would extend run time rather than shorten it.

A thermostat's cooling setpoint is satisfied but the indoor blower keeps running continuously. What is the first thing to check?

• a.Whether the compressor contactor has welded itself closed
• b.Whether the evaporator coil is frozen solid
• c.Whether the fan switch is set to ON rather than AUTO✓
• d.Whether the outdoor unit's capacitor has failed

A fan switch left in the ON position runs the blower continuously by design, and it is the simplest explanation to rule out first. A welded contactor would keep the compressor running, not just the blower. A frozen coil affects capacity and can extend run time but does not command continuous fan operation. And an outdoor capacitor failure affects the condenser, not the indoor blower.

You measure 197 volts at a condenser rated 208/230 volts while the compressor is trying to start. What is the concern?

• a.Low voltage will make the compressor run cooler and last longer
• b.Low voltage has no effect because the compressor is single phase
• c.Low voltage raises current draw and can overheat the windings✓
• d.Low voltage only matters on three-phase equipment

A motor delivering the same mechanical work at reduced voltage draws more current, and that extra current heats the windings. Low voltage does not make a motor run cooler. Single-phase compressors are just as vulnerable as three-phase, arguably more so at starting. And the effect is a property of induction motors generally, not of phase count.

A technician measures 240 volts across an open contactor's line terminals with the unit off and 0 volts across the contacts when it is pulled in. What does that indicate?

• a.The line voltage supply is unstable
• b.The contactor coil is open
• c.The contacts are burned and adding resistance
• d.The contactor is operating normally✓

Full voltage across an open contactor and no measurable drop across the closed contacts is exactly what a healthy contactor does. An open coil would prevent it from pulling in at all. Burned contacts would show a measurable voltage drop while closed. And these readings show a stable supply rather than an unstable one.

A technician performs annual maintenance on a residential split system. Which task most directly protects capacity on hot days?

• a.Replacing the thermostat batteries
• b.Tightening the electrical lugs at the disconnect
• c.Cleaning the outdoor coil and clearing the surrounding area✓
• d.Lubricating the blower motor's sealed bearings

A clean condenser with unobstructed airflow keeps condensing temperature and head pressure down, which is exactly what protects capacity when it is hottest. Tight electrical connections prevent failures but do not improve heat rejection. Sealed bearings are not field lubricated. And fresh thermostat batteries prevent nuisance outages but add no capacity.

During maintenance you find the outdoor coil packed with cottonwood. What is the correct cleaning approach?

• a.Brush the fins vigorously across their face with a wire brush
• b.Rinse from the inside out with low-pressure water after disconnecting power✓
• c.Spray a caustic cleaner and leave it on the coil to dry
• d.Blast the outside face of the coil with a pressure washer set at full pressure

Rinsing from the inside outward pushes debris back the way it came, and low pressure with the power off protects the fins and the technician. High-pressure washing folds fins flat and drives debris deeper. A wire brush across the face bends and tears the aluminum. And leaving a caustic cleaner to dry on the coil corrodes fins and tubing.

A customer replaced a 1-inch pleated filter with a high-MERV version and now complains the house is not cooling. What is the likely mechanism?

• a.Higher MERV filters remove humidity from the return air
• b.The added pressure drop cut airflow, reducing capacity✓
• c.The filter media has changed the refrigerant charge requirement
• d.The denser filter causes the compressor to short cycle on high pressure

A dense filter in a slot sized for a low-resistance one raises static pressure and drops airflow, which lowers capacity and can freeze the coil. Filter selection has no bearing on how much refrigerant the system holds. Filters capture particles, not water vapor. And the resulting problem shows up as low suction and possible icing rather than a high-pressure trip.

A homeowner asks why closing registers in unused rooms did not lower their bill. What is the correct explanation?

• a.Closed registers cause the compressor to run at reduced capacity
• b.Closing registers has no measurable effect on any other part of the duct system
• c.Closing registers raises system static pressure and can reduce total airflow✓
• d.Closed registers redirect air to the return and shorten run times

Closing outlets raises static pressure, which reduces total airflow and can push a system toward coil icing or high limit trips rather than saving energy. Compressor capacity is set by refrigerant conditions, not by damper position. Air blocked at a register does not usefully return to the equipment. And the effect is measurable, which is exactly why the practice causes problems.

A technician suspects duct leakage is hurting performance in an existing home. What test provides the evidence?

• a.An amp draw reading on the blower motor
• b.A combustion analysis at the furnace flue
• c.A temperature split reading at the coil
• d.A pressurized duct leakage test with a calibrated fan✓

A duct pressurization test measures leakage in CFM at a reference pressure, which is the direct evidence of how much conditioned air is escaping. Temperature split reflects the coil's performance, not the duct's tightness. Combustion analysis addresses the burner. And blower amperage responds to total system resistance without isolating leakage.

An older thermostat has a heat anticipator setting. What does it do?

• a.Adds a small heat source that shuts the burner off slightly early to limit overshoot✓
• b.Runs the blower before the burner to warm the ducts
• c.Prevents the compressor from starting within five minutes of shutdown
• d.Delays the burner start until the room has dropped a full degree

The anticipator warms the bimetal slightly so the contacts open before the room reaches setpoint, letting residual heat finish the job and reducing temperature swing. It does not add a starting delay based on room temperature. Pre-purging air through the ducts is a fan control function. And short-cycle protection for the compressor is a separate timing control.

A smart thermostat is installed on a system with no common wire, and it resets intermittently. What is the standard fix?

• a.Replace the thermostat with one rated for line voltage
• b.Run a common conductor or install a listed adapter at the equipment✓
• c.Increase the transformer's secondary voltage to 30 volts
• d.Move the thermostat to an exterior wall to improve its wireless signal

These thermostats need continuous 24-volt power, and either a dedicated common conductor or a manufacturer's adapter supplies it without power stealing. Transformers are not field adjustable and raising voltage would damage controls. Wall location affects temperature accuracy, not power supply. And residential systems use low-voltage controls, so a line-voltage thermostat is not an option.

A technician needs to confirm actual airflow on an installed system without a flow hood. Which method is most practical?

• a.Measure temperature rise on the furnace and calculate CFM from the output✓
• b.Estimate from the register face velocity multiplied by the grille free area
• c.Compare the amp draw to the blower motor's rated amps
• d.Read the nameplate CFM for the equipment model

With a known firing rate and efficiency, measuring the temperature rise and applying the sensible heat formula gives a reliable airflow figure with tools every technician carries. Register velocity estimates are crude and ignore the effective free area of the grille. Nameplate CFM is a rated value, not what the installed system delivers. And motor amperage varies with static in ways that do not translate directly to CFM.

A rooftop unit's economizer damper is stuck fully open on a 100 F day. What symptom will the building experience?

• a.The supply air will be colder than design
• b.The system will fail to hold setpoint as it conditions hot outdoor air✓
• c.The compressor will short cycle on low pressure
• d.The building will go strongly negative in pressure

An economizer stuck open in high ambient forces the coil to cool outdoor air at 100 F instead of return air, so capacity is consumed and the space drifts above setpoint. Supply air will be warmer, not colder. Suction pressure will be high with that hot air over the coil rather than low. And bringing in extra outdoor air pressurizes the building rather than making it negative.

A commercial rooftop unit trips its high-pressure switch every afternoon. Which cause should be checked first?

• a.An undersized return air filter rack
• b.A failed condensate overflow switch
• c.Condenser airflow, including a dirty coil or recirculated discharge air✓
• d.A shorted low-voltage thermostat cable

High-pressure trips that follow the outdoor temperature point to heat rejection, so a fouled coil, a failed condenser fan, or hot air recirculating from an adjacent unit lead the list. A shorted control cable would cause erratic operation or transformer failure. A restrictive filter rack lowers head pressure by starving the evaporator. And a condensate switch interrupts the call without producing a high-pressure trip.

How should a technician document a diagnosis that requires equipment replacement rather than repair?

• a.By noting only the model and serial number of the failed unit
• b.By recording the recommendation without the supporting measurements
• c.In writing, with the measured readings that support the conclusion✓
• d.Verbally, so the customer is not overwhelmed with technical detail

A written record of the readings, what they mean, and the recommendation protects the customer and the contractor and lets a second opinion be evaluated on the same evidence. A verbal explanation leaves nothing to review later. Nameplate data alone does not establish why the unit failed. And a recommendation without measurements is an opinion the customer cannot verify.

During a service call you find a heat exchanger with a visible crack. What is the appropriate immediate action?

• a.Seal the crack with high-temperature furnace cement and retest
• b.Shut the appliance down, tag it, and inform the customer in writing✓
• c.Reduce the manifold pressure to lower the exchanger temperature
• d.Leave it operating and schedule the replacement for the following week

A cracked heat exchanger can put combustion products into the supply air, so the appliance is taken out of service, tagged, and the condition documented for the customer. Patching a heat exchanger is not an approved repair. Lowering firing rate does not close the crack or stop the leakage path. And leaving it running for another week keeps a carbon monoxide hazard in operation.

Which scope of work falls within the C-20 Warm-Air Heating, Ventilating and Air-Conditioning classification?

• a.Installing the electrical service panel that feeds the equipment
• b.Installing the building's domestic water and sanitary drainage piping
• c.Installing the structural framing for a rooftop equipment platform
• d.Installing warm-air heating and air-conditioning systems, including their ducts and vents✓

The C-20 classification covers warm-air heating, ventilating, and air-conditioning systems together with the ducts, vents, and related components that make them complete. Service panel work is electrical contracting. Domestic water and drainage piping is plumbing. And structural framing for a platform belongs to a building or framing classification.16 CCR 832.20

A general contractor asks a C-20 contractor to also install the hydronic boiler and radiant piping. What is the correct response?

• a.Decline unless properly licensed, since that work falls under another classification✓
• b.Accept, provided the C-20 contractor pulls the mechanical permit
• c.Accept, because a hydronic system is a form of warm-air heating
• d.Accept, because all heating work falls under C-20

License classifications define the work each contractor may perform, and hydronic boilers and piping fall to a different classification than warm-air heating. Pulling a permit does not enlarge a license's scope. Being asked by a general contractor does not authorize out-of-scope work. And a hydronic system distributes heat through water rather than warm air, so it is not the same category of work.

Under California's minor work exemption, an unlicensed person may perform a project only when the total value of labor and materials is below what threshold?

• a.Five thousand dollars
• b.One thousand dollars✓
• c.Twenty-five hundred dollars
• d.Five hundred dollars

The minor work exemption applies to projects below one thousand dollars in combined labor and materials, and only when the work is casual and does not require a permit. The five hundred dollar figure is the older threshold that was raised. The twenty-five hundred and five thousand dollar figures are well above the exemption and describe work that clearly requires a license.Business and Professions Code 7048

A homeowner asks a technician to install a small ductless head for $850 cash with no permit. Why does the minor work exemption not apply?

• a.Because the work involves refrigerant, which is always regulated
• b.Because the customer is paying cash rather than by check
• c.Because the installation requires a permit, which disqualifies the exemption✓
• d.Because the job is under a thousand dollars and therefore exempt

The exemption requires that the work be casual and minor and that no building permit be required, so a permitted mechanical installation falls outside it regardless of price. Refrigerant handling is regulated by the EPA but is not what defeats the exemption. The form of payment has no bearing on licensing. And being under the dollar threshold is only one of the conditions, not the whole test.Business and Professions Code 7048

A licensed C-20 contractor's employee will install rooftop units. What does the CSLB require of that employee?

• a.A separate C-20 license in the employee's own name
• b.No separate license, because the employer's license covers employees✓
• c.Registration as a home improvement salesperson
• d.A qualifying individual designation added onto the employer's license

Employees working for a licensed contractor perform work under that license and are not separately licensed. A worker does not need to hold a license of their own to be employed by a licensee. Home improvement salesperson registration applies to those who solicit and negotiate contracts, not to installers. And a qualifying individual is the person whose experience qualifies the license, a role only one or a few people fill.

A contractor takes a deposit and does no work for months. What CSLB concern does this raise?

• a.Abandonment and excessive down payment rules apply to home improvement contracts✓
• b.It is permitted as long as the total contract price exceeds the deposit by tenfold
• c.It affects the contractor's workers' compensation classification
• d.It requires the contractor to obtain a second bond

Home improvement contract rules limit down payments and treat unexplained abandonment as grounds for discipline. Workers' compensation classification concerns payroll and risk, not deposits. There is no ten-to-one rule that legitimizes an oversized deposit. And a second bond is not the remedy for abandoning a job.

Why does a residential HVAC change-out generally require a permit and inspection even when the new equipment matches the old?

• a.Because the work is regulated construction affecting life safety and energy compliance✓
• b.Because the utility requires a permit before restoring gas service
• c.Because permits are what establish the contractor's warranty obligations
• d.Because inspections determine the equipment's efficiency rating

Combustion venting, electrical connections, and energy compliance all bear on occupant safety, which is why the jurisdiction reviews and inspects the work. Warranty obligations arise from the contract and the manufacturer, not from the permit. Gas service is not routinely shut off and restored for a change-out. And efficiency ratings are established by laboratory testing, not by a field inspector.

A technician must service a rooftop unit's blower compartment. Which Cal/OSHA procedure applies before reaching into the cabinet?

• a.Fall protection anchorage point inspection
• b.Confined space entry permitting
• c.Lockout and tagout of the energy source✓
• d.Respiratory protection fit testing

Servicing machinery where unexpected startup could injure the worker requires the energy source to be locked out and tagged. Confined space rules apply to spaces with restricted entry and hazardous atmospheres, not to a blower compartment reached from outside. Respirator fit testing applies where respiratory hazards are present. And fall protection addresses working near the roof edge, not the cabinet itself.Cal/OSHA, Title 8 CCR

Two technicians are working on the same rooftop unit. How should lockout be handled?

• a.One lock applied by the lead technician covers both workers
• b.Each authorized worker applies a personal lock to the energy isolating device✓
• c.A tag alone is sufficient when two workers can see each other
• d.The lock is applied by whoever arrives at the disconnect first

Group lockout requires each exposed worker to apply their own lock so no one can be re-energized by another person's decision. A single lead's lock leaves the second worker dependent on someone else. Assigning the lock by who arrives first has no relation to who is exposed. And a tag without a lock provides warning but no physical prevention.Cal/OSHA, Title 8 CCR

A technician sets an extension ladder to reach a roof. What setup practice is required?

• a.Extend it about three feet above the landing and secure it✓
• b.Place the feet on a sheet of plywood over soft ground and leave it unsecured
• c.Set it at a 30 degree angle so it is easy to climb
• d.Rest the top rung directly on the gutter for stability

A ladder used for roof access extends above the landing surface so the climber has something to hold, and it must be secured against displacement. A 30 degree angle is far too shallow and invites the base to slide out. Gutters are not designed to carry ladder loads and will collapse. And plywood may spread the load but does nothing to prevent the ladder from shifting.Cal/OSHA, Title 8 CCR

What angle should a straight or extension ladder be set at for safe use?

• a.One foot out for every one foot of working length
• b.One foot out for every two feet of working length
• c.One foot out for every three feet of working length
• d.One foot out for every four feet of working length✓

The four-to-one rule places the base one quarter of the working length away from the wall, giving a stable climbing angle of about 75 degrees. A one-to-one setup is dangerously shallow and slides out. A one-to-two setup is still far too shallow. And one-to-three is closer but still outside the accepted ratio.Cal/OSHA, Title 8 CCR

A technician is working near the unprotected edge of a commercial roof. What does Cal/OSHA require?

• a.Fall protection appropriate to the height and exposure of the work✓
• b.High-visibility clothing to mark the worker's position
• c.A written notice posted at the roof access hatch
• d.A second worker standing by to watch the edge

Work at height near an unprotected edge requires guardrails, a personal fall arrest system, or another accepted method of fall protection. A spotter provides no physical protection if the worker slips. High-visibility clothing helps others see the worker but does not stop a fall. And posted notices inform but do not protect.Cal/OSHA, Title 8 CCR

Under California's heat illness prevention standard, what must an employer provide to outdoor workers on a hot day?

• a.A medical examination before each summer season
• b.A weekly safety meeting covering heat topics
• c.Salt tablets and electrolyte supplements stocked at the job trailer
• d.Access to potable water and shade, plus training and rest breaks✓

The standard requires enough fresh drinking water, access to shade when temperatures reach the trigger, training on heat illness, and the ability to take preventive cool-down rests. Weekly meetings are good practice but are not the specific requirement. Salt tablets are not required and can be harmful. And pre-season medical exams are not part of the standard.Cal/OSHA, Title 8 CCR 3395

A crew member on a rooftop becomes confused and stops sweating on a very hot afternoon. What is the correct response?

• a.Treat it as a medical emergency, call for help, and begin cooling✓
• b.Give them water and let them continue at a slower pace
• c.Move them into the truck's air conditioning and resume work after a break
• d.Have them rest in the shade and check back in an hour

Confusion with hot dry skin points to heat stroke, which is life threatening and requires emergency services plus immediate active cooling. Continuing to work at any pace risks death. Simply sitting in a cool truck without emergency care delays treatment. And waiting an hour to check back is exactly the delay that makes heat stroke fatal.Cal/OSHA, Title 8 CCR 3395

A technician is brazing in a residential attic. Which precaution addresses the greatest hazard of that task?

• a.Grounding the torch handle to the copper tubing
• b.Wearing a face shield to guard against refrigerant splash
• c.Wearing hearing protection during torch operation
• d.Clearing combustibles, using a fire barrier, and maintaining a fire watch✓

Hot work in an attic full of insulation, framing, and paper facing carries a real fire risk, so combustibles are cleared, a barrier is used, and someone watches for smoldering afterward. Torch work is not a significant noise hazard. Refrigerant splash is a concern during charging, not during brazing on an evacuated line. And grounding a torch handle serves no purpose in this operation.

Why must brazing be done with ventilation when working on refrigerant lines?

• a.Brazing consumes so much oxygen that the working space becomes oxygen deficient
• b.The nitrogen purge displaces breathable air throughout the room
• c.Silver alloy releases mercury vapor when it reaches melting temperature
• d.Heated refrigerant residue and flux fumes produce toxic decomposition products✓

Residual refrigerant and flux exposed to a flame break down into irritating and toxic compounds that must be carried away from the technician. A torch does consume oxygen, but ordinary rooms do not become oxygen deficient from brazing alone. The small nitrogen trickle used for purging does not displace the air in a room. And silver brazing alloys used in this work do not contain mercury.

How should oxygen and acetylene cylinders be stored on a service truck?

• a.Standing upright with the regulators left attached for quick use
• b.Laid horizontally together so they cannot tip over
• c.Stored together in a sealed compartment with no ventilation to keep them dry
• d.Secured upright with valve caps in place and the two gases separated✓

Fuel gas and oxygen cylinders are kept upright and secured, with caps on and separation between the two gases, so a leak or valve break cannot create a fire. Storing acetylene on its side lets acetone migrate out of the cylinder. Leaving regulators attached during transport exposes them to damage. And a sealed unventilated compartment allows any leak to accumulate.

Why must a pressure regulator with a relief device be used when pressure testing with nitrogen?

• a.Because the regulator converts the nitrogen into a usable testing mixture
• b.Because nitrogen is flammable at high pressure
• c.Because full cylinder pressure far exceeds the system's rated pressure✓
• d.Because the cylinder cannot be shut off once opened

A nitrogen cylinder holds pressure in the thousands of psi, which would rupture a coil or line set instantly, so a regulator with a relief valve limits what reaches the system. Nitrogen is inert and does not burn. Cylinder valves close normally, so shutoff is not the issue. And a regulator reduces pressure rather than changing the composition of the gas.

A large refrigerant release occurs in a mechanical room. What is the primary hazard to a technician inside?

• a.Explosion of the refrigerant vapor at normal room temperature
• b.Immediate chemical burns from vapor contact with skin
• c.Oxygen displacement leading to asphyxiation in a low area✓
• d.Corrosion of tools and instruments in the room

Refrigerant vapor is heavier than air and pools in low areas, pushing out breathable air and causing asphyxiation before a person recognizes the danger. Vapor contact does not burn skin, though liquid contact causes frostbite. Corrosion is a slow equipment issue, not an immediate personal hazard. And traditional refrigerants are not explosive at room temperature, though A2L refrigerants are mildly flammable and carry their own precautions.

Liquid refrigerant sprays onto a technician's forearm during a hose disconnect. What is the correct first aid?

• a.Rub the area briskly to restore circulation
• b.Flush the area with lukewarm water and seek medical evaluation✓
• c.Apply direct heat from a heat gun until the frozen tissue rewarms
• d.Wrap the arm tightly and wait for sensation to return

Rapid evaporation causes a frostbite injury, and gentle rewarming with lukewarm water followed by medical evaluation is the accepted response. Rubbing frozen tissue causes further mechanical damage. Direct heat can burn tissue that has lost sensation. And tight wrapping restricts circulation and worsens the injury.

What personal protective equipment is appropriate when charging or recovering refrigerant?

• a.A full-face respirator and chemical apron
• b.A flame-resistant coverall and welding hood
• c.Hearing protection and a hard hat
• d.Safety glasses and gloves rated for refrigerant contact✓

Eye protection and appropriate gloves guard against the frostbite and eye injury that a liquid release can cause. Full-face respirators and chemical aprons address hazards well beyond ordinary charging in a ventilated space. Hearing protection and a hard hat address noise and overhead hazards. And welding gear belongs to hot work, not to refrigerant handling.

A technician finds pipe insulation on old ductwork in a 1960s building that may contain asbestos. What is the correct action?

• a.Encapsulate it with duct mastic and continue the installation
• b.Wet it down and dispose of it in the regular jobsite dumpster
• c.Remove it carefully while wearing a dust mask
• d.Stop work in that area and have the material assessed by qualified personnel✓

Suspect asbestos-containing material must be left undisturbed until it is tested and handled by trained and certified personnel. A dust mask offers no meaningful protection against asbestos fibers. Wetting reduces dust but does not authorize an untrained person to remove or dispose of it. And covering it with mastic disturbs the material and is not an approved encapsulation method.

A technician smells gas at a furnace closet on arrival. What is the correct first action?

• a.Use a lighter to check the joints for the leak source
• b.Light the burner to burn off the accumulated gas
• c.Turn on the exhaust fan to clear the closet
• d.Shut off the gas, avoid creating ignition sources, and ventilate✓

Isolating the fuel and avoiding any spark or flame while ventilating naturally is the first priority when gas has accumulated. Switching on an exhaust fan operates an electrical device that can arc in a flammable atmosphere. Lighting the appliance introduces an ignition source into the very condition being investigated. And an open flame near suspected joints is the most dangerous possible leak test.

Why is carbon monoxide from a malfunctioning furnace especially dangerous to occupants?

• a.It is colorless and odorless and binds to hemoglobin far more readily than oxygen✓
• b.It has a strong sulfur odor that occupants ignore over time
• c.It becomes hazardous only above 2,000 parts per million in the space
• d.It is heavier than air and settles into basements, where it becomes visible as a haze

Carbon monoxide gives no warning to the senses and takes the place of oxygen on hemoglobin, so people are impaired before they know anything is wrong. It has a density close to that of air and is never visible. The sulfur odor associated with natural gas comes from an added odorant, not from carbon monoxide. And harmful health effects occur at levels far below 2,000 parts per million, especially with long exposure.

Where should a carbon monoxide alarm be located in a dwelling with fuel-burning appliances?

• a.In the garage near the vehicle parking area only
• b.Inside the furnace closet, directly above the burner compartment access door
• c.Outside each separate sleeping area and on every level of the dwelling✓
• d.Immediately adjacent to the kitchen range hood

Alarms are placed outside sleeping areas and on each level so occupants are warned while they sleep, which is when carbon monoxide is most dangerous. Mounting one inside the furnace closet produces nuisance alarms and does not protect the bedrooms. A garage-only alarm leaves the living space unmonitored. And placement next to a cooking appliance invites false alarms from normal cooking byproducts.

A house with a new tight envelope shows backdrafting at the water heater when the clothes dryer and range hood run. What is the underlying cause?

• a.The vent connector is sloped too steeply toward the chimney
• b.The water heater's gas pressure is set too low
• c.Exhaust appliances are depressurizing the house below what the vent can overcome✓
• d.The furnace's blower is running at too high a speed

Exhaust fans remove more air than can leak back into a tight house, and the resulting negative pressure overwhelms a natural-draft appliance's weak draft. Low gas pressure produces a small flame rather than reversed flow in the vent. A steeper upward slope improves draft rather than harming it. And the furnace blower moves air within the house without pulling it out of the building.

Which test would a technician use to confirm that a natural-draft appliance is drafting properly under worst-case conditions?

• a.A refrigerant leak search around the appliance
• b.A duct leakage test with the registers sealed
• c.A spillage test at the draft hood with exhaust appliances running✓
• d.A manifold gas pressure reading at full fire

Running the house's exhaust appliances and then checking for spillage at the draft hood reproduces the worst-case depressurization the appliance will face. Duct leakage testing measures the distribution system, not appliance draft. Refrigerant leak searching addresses the cooling circuit. And manifold pressure confirms the firing rate but says nothing about whether flue gases leave the building.

What is the purpose of a flammable vapor ignition resistant design on an appliance installed in a garage?

• a.To prevent gasoline vapors near the floor from being ignited by the burner✓
• b.To let the appliance draw combustion air from the garage safely
• c.To keep the appliance operating during a power outage
• d.To allow the appliance to be installed without a vent

The listing addresses the specific hazard of gasoline vapors collecting at floor level, which is why an appliance with that design may be installed without elevating the ignition source. It has nothing to do with power outages. Venting is still required for any fuel-burning appliance. And drawing combustion air from a garage remains a separate concern addressed by the appliance's air source.

What is the primary purpose of the appliance clearance and access requirements in the mechanical code?

• a.To ensure that ductwork can be replaced without first removing the appliance
• b.To allow safe service and to keep heat away from combustible construction✓
• c.To standardize equipment cabinet dimensions across manufacturers
• d.To guarantee the equipment meets its published efficiency rating

Clearances protect adjacent construction from heat while access provisions let a technician reach and service the equipment safely. Cabinet dimensions are set by manufacturers, not by clearance rules. Duct replacement convenience is not the objective. And field clearances do not determine a laboratory efficiency rating.California Mechanical Code (Title 24, Part 4)

Which code primarily governs the installation of ductwork, venting, and mechanical equipment in California?

• a.The California Mechanical Code, Title 24 Part 4✓
• b.The California Plumbing Code, Title 24 Part 5
• c.The California Building Code, Title 24 Part 2
• d.The California Fire Code, Title 24 Part 9

The California Mechanical Code is the part of Title 24 that governs mechanical systems, including ducts, vents, and equipment installation. The Building Code addresses structural and general building provisions. The Plumbing Code covers water and drainage systems. And the Fire Code addresses fire protection systems and hazardous operations.California Mechanical Code (Title 24, Part 4)

Which part of Title 24 sets the energy efficiency requirements that affect HVAC equipment and duct sealing?

• a.Part 2, the Building Code
• b.Part 3, the Electrical Code
• c.Part 4, the Mechanical Code
• d.Part 6, the Energy Code✓

Part 6 contains California's energy efficiency standards, which drive duct sealing verification, equipment efficiency, and compliance documentation. Part 2 covers general building construction. Part 3 governs electrical installations. And Part 4 covers mechanical installation requirements but is not the energy standard.

What is the role of a HERS rater on a California residential HVAC alteration?

• a.To certify the contractor's license status with the CSLB
• b.To independently field-verify measures such as duct leakage and airflow✓
• c.To issue the mechanical permit on behalf of the local building department
• d.To design the duct system and select the equipment

A HERS rater is a third party who tests and documents specified measures so the compliance claim is verified by someone other than the installer. Permits are issued by the local building department. Design and equipment selection are the contractor's or designer's responsibility. And license verification is a CSLB function, not a rater's.

Why must return air not be drawn from a bathroom, closet, or garage?

• a.Because moisture, contaminants, or vehicle exhaust would be distributed through the house✓
• b.Because those rooms rarely have a supply register to balance against
• c.Because those spaces are usually too small to supply enough air
• d.Because the return grille would violate the room's fire rating

Air pulled from these spaces carries moisture, chemicals, or combustion products into the return and then into every room the system serves. Room size is a design consideration but not the reason for the prohibition. Whether a supply register exists does not change the contaminant issue. And most such rooms are not fire rated, so a rating violation is not the basis of the rule.

A technician needs to enter a crawl space to service ductwork. What hazard assessment applies?

• a.It is a permit-required confined space in every case
• b.It may be a confined space, requiring evaluation of atmosphere and access✓
• c.It is only a confined space when standing water is present
• d.It is exempt from any evaluation because it is underneath the customer's home

A crawl space has limited entry and exit and is not designed for continuous occupancy, so it must be evaluated for atmospheric hazards, engulfment, and access before entry. Being residential does not exempt a space from evaluation. Not every crawl space rises to permit-required status; that depends on the hazards found. And standing water is one possible hazard among several, not the sole test.

What must be tested before entry into a permit-required confined space?

• a.Ambient noise level and lighting adequacy
• b.Relative humidity and dew point of the space
• c.Oxygen content, flammable gases, and toxic contaminants✓
• d.Structural load capacity of the floor joists and the decking

Atmospheric testing checks oxygen level first, then flammable gas concentration, then toxic contaminants, in that order. Noise and lighting are working conditions but not atmospheric hazards. Structural capacity matters for access planning, not atmospheric testing. And humidity is a comfort parameter with no bearing on the entry hazard.

A technician must take a voltage reading inside an energized panel. What practice reduces the risk?

• a.Remove watches and rings only, since jewelry is the main hazard
• b.Use rated meter leads and PPE, keep one hand clear, and stand on a dry surface✓
• c.Have a helper hold the panel cover to improve visibility
• d.Work quickly so exposure time is minimized

Properly rated test equipment, appropriate protective equipment, avoiding a hand-to-hand current path, and standing on a dry insulating surface together address shock and arc hazards. Removing jewelry helps but is only one small piece. Speed does not reduce the severity of a fault. And a helper holding a metal cover adds a second person into the hazard zone.

What does an arc flash hazard in an electrical panel primarily produce?

• a.A slow buildup of heat that trips the breaker well before injury occurs
• b.A magnetic field that damages test instruments
• c.A sustained current path through the equipment ground
• d.An intense release of heat and pressure that can burn a nearby worker✓

An arc flash releases enormous energy in milliseconds, producing burns, blast pressure, and molten metal well beyond the point of the fault. Breakers do not always clear fast enough to prevent injury. Magnetic effects exist but are not the injury mechanism. And a sustained ground path describes a ground fault, not the arc flash event itself.

A technician is cutting an opening in an old plaster ceiling for a return grille and creates heavy dust. What hazard should be considered?

• a.Static electricity generated by the cutting tool
• b.Only the risk of damage to the customer's furnishings and floors
• c.Respirable dust that may contain silica or lead-based paint✓
• d.Only the risk of eye irritation from large particles

Old building materials can contain crystalline silica and lead-based paint, and the fine airborne fraction is what reaches the lungs or is ingested. Eye irritation is real but is the least of the health concerns. Protecting furnishings is a workmanship matter, not a health hazard. And static from a cutting tool is not a recognized hazard in this task.

Where does a technician find the health hazards and handling requirements for a chemical coil cleaner?

• a.On the product's safety data sheet✓
• b.On the equipment manufacturer's installation instructions
• c.On the CSLB's license classification page
• d.In the California Mechanical Code appendix

A safety data sheet lists composition, health effects, protective equipment, first aid, and disposal for that specific product, and it must be available to workers who use it. Equipment installation instructions cover the appliance, not the chemicals a technician brings. The mechanical code regulates installations, not chemical products. And license classification pages describe scope of work.

A supply duct penetrates a garage ceiling that separates the garage from the dwelling. What construction requirement applies?

• a.The duct must include a manual damper at the penetration
• b.The duct must be lined with fiberglass on the interior surface
• c.The duct must be of a material and construction that maintains the required separation✓
• d.The duct must be increased one size where it passes through

Ducts crossing the garage separation must be constructed so the separation between the garage and the dwelling is maintained, and no openings may be made into the garage. Interior lining is an acoustic or thermal choice with no bearing on the separation. A manual damper is a balancing device, not a rated assembly. And upsizing at a penetration serves no code purpose.

Why is it prohibited to install a supply or return opening in a garage that connects to the dwelling's duct system?

• a.Because the garage door creates pressure fluctuations in the duct
• b.Because vehicle exhaust and stored chemicals could be carried into living areas✓
• c.Because garage temperatures would damage the ductwork over time
• d.Because the garage is not conditioned space and would waste energy

Any opening between the garage and the duct system provides a direct path for carbon monoxide and chemical vapors to reach bedrooms and living spaces. Energy waste is a real but secondary consequence. Garage temperature swings do not damage properly installed duct. And door movement creates minor pressure changes that are not the basis of the prohibition.

A technician plans to work alone servicing rooftop units at a vacant commercial building. What safety provision matters most?

• a.A check-in procedure so someone knows the location and expected return✓
• b.Parking the service vehicle where it is clearly visible from the street
• c.Bringing a second set of gauges in case one fails
• d.Wearing a company uniform so occupants can identify the worker

Working alone at height with energized equipment and refrigerant means an injury will go undiscovered unless someone knows where the technician is and when to expect contact, so a scheduled check-in is the provision that actually shortens response time. Backup gauges address downtime, not injury. Vehicle placement does not summon help if the technician is unconscious on a roof. And a company uniform aids identification in an occupied building, which this one is not.

An HVAC company must maintain workers' compensation coverage under California contractor law. What does that coverage do?

• a.It pays medical costs and lost wages for employees injured on the job✓
• b.It insures the customer against defective workmanship
• c.It covers property damage the contractor causes on a job
• d.It replaces the contractor's bond obligation to the CSLB

Workers' compensation is employee injury coverage, paying medical treatment and wage replacement without regard to fault. The contractor's bond is a separate financial security posted with the board. Workmanship defects are addressed by contract, warranty, and the bond. And third-party property damage falls under general liability insurance.

A customer signs a residential change-out contract at their kitchen table. What consumer protection generally applies?

• a.A requirement that the contractor finance the project at no interest
• b.An automatic extension of the manufacturer's warranty to ten years
• c.A guarantee that the equipment will be installed within ten days
• d.A right to cancel the contract within a defined period after signing✓

Home solicitation contracts signed away from the contractor's place of business carry a statutory right to cancel within a defined window, and the notice must be given to the buyer. No law fixes a ten-day installation deadline. Warranty length is set by the manufacturer and the contract. And there is no requirement that a contractor provide interest-free financing.

Why must a technician verify that the correct refrigerant is being added to a system?

• a.Because mixing refrigerants voids the equipment's efficiency rating
• b.Because mixed refrigerants cannot be recovered or reclaimed and change system pressures✓
• c.Because different refrigerants require different gauge hose colors
• d.Because the wrong refrigerant will not pass through the metering device

A cross-charged system produces unpredictable pressures and creates a mixture that no reclaimer will accept, so the entire charge becomes waste. Efficiency ratings are a secondary concern next to the safety and disposal problem. Hose color is a convention, not a technical requirement. And the wrong refrigerant flows through a metering device perfectly well, which is exactly why the error is not self-correcting.

A technician is asked to sign off on a job installed by someone else without inspecting it. What is the professional obligation?

• a.Sign if the customer accepts responsibility for the work in writing
• b.Sign and note on the invoice that the work was not observed
• c.Sign if the other installer is also licensed under the same classification
• d.Decline unless the work is actually inspected and verified✓

Certifying work means attesting to its condition, which cannot be done without inspecting it, and a false certification exposes both the public and the license. Another person's license does not transfer verification responsibility. A customer cannot waive a safety certification obligation. And a disclaimer on an invoice does not cure a certification that was never based on observation.