CSLB HVAC (C-20) Trade — All Questions

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.

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.