CSLB General Building (B) — All Questions

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

• a.To cool the electronic controls
• b.To supply oxygen for complete and safe fuel combustion✓
• c.To increase supply air temperature
• d.To reduce refrigerant 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 near the floor
• b.Both in the ceiling
• c.One opening near the top and one near the bottom of the space✓
• d.One 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 only
• b.Listed gas appliances with draft hoods or Category I equipment✓
• c.Solid-fuel wood stoves
• d.High-temperature incinerators

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 system efficiency
• b.To prevent water damage and dispose of condensate safely✓
• c.To raise refrigerant subcooling
• d.To supply combustion air

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
• b.In a basement with a floor drain
• c.In an attic or above a finished ceiling where leakage would cause damage✓
• 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 refrigerant charge
• b.Prevent oxidation and scale formation inside the tubing✓
• c.Increase joint temperature
• d.Test the thermostat

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
• b.To prevent refrigerant leaks
• c.To reduce heat gain and prevent condensation on the cold line✓
• d.To increase line pressure

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 airflow measurement
• b.To prevent overheating of nearby combustible materials and reduce fire risk✓
• c.To lower the refrigerant charge
• d.To allow duct expansion only

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 of the insulation
• b.The length of the thermostat wire
• c.The manufacturer's specifications for the system capacity and line length✓
• d.The size of the electrical 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 larger condensate trap
• b.Correct line sizing to maintain adequate refrigerant velocity✓
• c.Extra thermostat wire
• d.A bigger air filter

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 refrigerant into the evaporator
• b.To change the direction of refrigerant flow between heating and cooling✓
• c.To drain condensate
• d.To regulate gas pressure

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 has no compressor
• b.It cannot be used for cooling
• c.All major components are contained in a single outdoor cabinet✓
• d.It requires no 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 refrigerant line size
• b.Deliver adequate gas volume at the required pressure to all connected appliances✓
• c.Reduce electrical load
• d.Support 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 gas pressure
• b.To vent excess gas
• c.To catch moisture and debris before they enter the appliance control valve✓
• d.To measure gas flow

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.The condensate is flowing
• b.Correct voltage, polarity, and secure grounding per the wiring diagram✓
• c.The refrigerant subcooling
• d.The duct insulation R-value

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
• b.Filter the supply air
• c.Reduce the transmission of vibration and noise into the duct system✓
• d.Add refrigerant capacity

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 gas pressure
• b.To prevent air leakage that wastes energy and reduces delivered airflow✓
• c.To hold refrigerant
• d.To support the furnace weight

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 usage
• b.Correct refrigerant type
• c.Unrestricted airflow across the condenser coil and service access✓
• d.Reduced thermostat wire length

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 access needed
• b.A refrigerant recovery machine
• c.A passageway, working platform, and light near the appliance✓
• d.A second gas meter

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
• b.Prevent air from being pulled through the drain and allow proper condensate flow✓
• c.Increase blower speed
• d.Filter the return air

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 them unsupported
• b.Support only at the equipment
• c.Provide supports at intervals to prevent sagging and maintain proper drain slope✓
• d.Bury them without 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 testing
• b.Pressure tested for leaks, then evacuated to remove moisture and non-condensables✓
• c.Filled with water
• d.Left open to atmosphere

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
• b.Into an open crawl space
• c.At an approved location outdoors with required clearances from openings✓
• d.Into the return duct

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 electrical panel only
• b.Within sight of and readily accessible to the outdoor unit✓
• c.In the attic
• d.Behind the condenser coil

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
• b.To insulate the line
• c.To remove moisture and trap contaminants circulating in the refrigerant✓
• d.To increase suction 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
• b.A garage or other space where it could pick up combustion products or flammable vapors✓
• c.A conditioned bedroom
• d.A central living room

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 toward the building
• b.Level and on a stable base that keeps the unit off the ground✓
• c.Directly on loose soil
• d.Tilted so condensate pools under 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.