CSLB General Building (B) — All Questions
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What is the primary function of a run capacitor on a single-phase motor?
- a.To fuse the circuit
- b.To improve motor efficiency and provide a phase shift for smoother running✓
- c.To ground the motor
- d.To measure airflow
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
- b.Regulate refrigerant flow
- c.Provide a high momentary boost of starting torque, then drop out of the circuit✓
- d.Filter the supply air
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
- b.Switches line-voltage power to the compressor and fan when energized by the control circuit✓
- c.Drains condensate
- d.Adjusts blower 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
- b.Rising head pressure and possible high-pressure or overload trip✓
- c.Increased subcooling only
- d.Lower amp draw on the compressor
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 at the coil
- b.Higher supply air temperature
- c.A cold, possibly frozen coil and low suction pressure✓
- d.Higher condenser airflow
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.Furnace heating efficiency
- b.The seasonal cooling efficiency of air-conditioning equipment✓
- c.The refrigerant type
- d.The duct leakage rate
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.Continuous cooling
- b.The burners light then shut off after a few seconds (flame loss)✓
- c.High head pressure
- d.Frozen evaporator
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
- b.Gas manifold pressure
- c.Total external static pressure across the air handler✓
- d.Condenser saturation temperature
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 every visit
- b.Replacing the compressor annually
- c.Regularly replacing or cleaning air filters and cleaning coils✓
- d.Removing the condensate trap
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 perfectly healthy compressor
- b.A mechanical or electrical problem such as high head pressure or failing windings✓
- c.An oversized filter
- d.Low thermostat voltage
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
- b.A dirty air filter
- c.A loss of power, a failed contactor, or an open safety/control circuit✓
- d.Excess superheat
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 requires no electricity
- b.Variable speed operation and improved energy efficiency✓
- c.It eliminates the need for ductwork
- d.It removes refrigerant 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
- b.The air filter
- c.The reversing valve or its solenoid coil✓
- d.The supply registers
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.