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.