Air Conditioning Repair Electrical Components and Controls Questions and Answers

Question 1

A technician responds to a no-cool call.
The indoor blower is running, and the thermostat is calling for cooling, but the outdoor unit is silent except for a faint humming sound.
The condenser fan is not spinning.
Which of the following is the MOST likely cause of this specific symptom?

Accepted Answer

A failed dual-run capacitor

Answer

A tripped circuit breaker for the condensing unit

Answer

A faulty thermostat

Answer

A stuck reversing valve

Question 2

Which of the following electrical safety devices is designed to open the control circuit and shut down the compressor in the event of a restricted condenser coil or a failed condenser fan motor?

Accepted Answer

A high-pressure safety switch

Answer

A low-pressure cutout switch

Answer

A crankcase heater

Answer

A time-delay relay

Question 3

A technician is installing a new thermostat for a heat pump system. To ensure the reversing valve is energized when the thermostat is set to 'Cool', to which terminal should the corresponding wire be connected?

Accepted Answer

O/B

Answer

Y

Answer

G

Answer

W

Question 4

A technician measures 240V at the line-side terminals (L1/L2) of a contactor and 24V across the coil terminals. However, there is 0V at the load-side terminals (T1/T2) and the compressor is not running. What is the most probable fault?

Accepted Answer

The contactor is faulty.

Answer

The control transformer has failed.

Answer

The circuit breaker is tripped.

Answer

The compressor windings are open.

Question 5

In a compressor circuit that utilizes a potential relay, what is the relay's primary function?

Accepted Answer

To disconnect the start capacitor from the circuit once the motor approaches full speed.

Answer

To protect the compressor from low voltage conditions.

Answer

To delay the restart of the compressor after a power interruption.

Answer

To energize the condenser fan motor simultaneously with the compressor.

Question 6

A technician is troubleshooting a system where the thermostat display is blank and there is no response from any HVAC function. Voltage measurement at the air handler's control board shows 120V entering the primary side of the control transformer, but 0V on the secondary side. What is the correct diagnosis?

Accepted Answer

The control transformer has failed.

Answer

The main circuit breaker for the house is tripped.

Answer

The thermostat is defective.

Answer

There is a short in the low-voltage wiring somewhere in the system.