FREE Air Conditioning Repair Electrical System Troubleshooting Questions and Answers

Question 1

A technician is troubleshooting a residential split-system AC unit.
The indoor fan runs, but the outdoor unit (condenser fan and compressor) does not energize.
A quick check shows 24V AC at the 'Y' terminal on the indoor control board and at the low-voltage wires going to the outdoor unit, but no 24V at the contactor coil in the outdoor unit.
What is the most likely component failure?

Accepted Answer

Contactor coil in the outdoor unit

Answer

Capacitor for the compressor

Answer

Thermostat wiring short

Answer

High-pressure switch

Question 2

When diagnosing a 'no cool' call, a technician finds that the compressor is humming loudly but not starting, and the condenser fan motor is running normally. The run capacitor for the compressor tests good. What is the most probable electrical issue?

Accepted Answer

Shorted start winding in the compressor

Answer

Failed condenser fan motor

Answer

Open thermal overload protector in the compressor

Answer

Failed start relay

Question 3

A technician is checking the resistance of a single-phase compressor motor windings. The readings are: Common to Run (C-R) = 2.5 ohms, Common to Start (C-S) = 4.0 ohms, and Run to Start (R-S) = 6.5 ohms. What do these readings indicate about the windings?

Accepted Answer

The compressor windings are healthy.

Answer

The compressor windings are shorted to ground.

Answer

The compressor windings are open.

Answer

The compressor has a faulty internal overload.

Question 4

Which of the following is the most effective diagnostic tool for identifying an intermittent electrical fault, such as a loose wire or a failing relay contact, that only occurs under specific operating conditions (e.g., when the unit vibrates or heats up)?

Accepted Answer

Data logger / recording multimeter

Answer

Megohmmeter

Answer

Clamp-on ammeter

Answer

Non-contact thermometer

Question 5

During a routine inspection, a technician notices that the insulation on the wiring connecting the compressor to the contactor is brittle and cracked. The system is still operating. What is the immediate safety concern and recommended action?

Accepted Answer

Risk of electrical shock or short circuit; de-energize and repair/replace wiring.

Answer

The compressor will immediately fail; replace the compressor.

Answer

Increased energy consumption; advise the customer about higher bills.

Answer

Reduced cooling capacity; recharge the refrigerant.

Question 6

A technician is troubleshooting a residential split-system AC unit.
The indoor fan runs, but the outdoor unit (condenser fan and compressor) does not energize.
A quick check shows 24V AC at the 'Y' terminal on the indoor control board and at the low-voltage wires going to the outdoor unit, but no 24V at the contactor coil in the outdoor unit.
What is the most likely component failure?

Accepted Answer

Faulty start capacitor

Answer

Open high-pressure switch

Answer

Shorted condenser fan motor

Answer

Failed contactor coil