Air Conditioning Repair Electrical Components and Controls 4

Question 1

A variable-speed ECM blower motor is not responding to a speed signal from the control board. After confirming 24V supply to the module, what is the next step?

Accepted Answer

Check the PWM or DC analog signal wire from the board to the motor module

Answer

ECM motors receive a speed-control signal (PWM or 0–10V DC) from the board; loss of this signal causes the motor to default to a fixed speed or stop.

Question 2

What is the correct procedure for discharging a capacitor before handling it?

Accepted Answer

Use a 10,000-ohm, 10-watt resistor across the terminals

Answer

A resistor safely dissipates the stored charge without the arc that a direct short causes, which can damage terminals and capacitor internals.

Question 3

Which component in a gas furnace/AC system directly controls when the indoor blower comes on after heating ignition?

Accepted Answer

Fan limit switch or control board fan delay

Answer

A fan limit switch or control board fan-delay timer delays blower startup until the heat exchanger warms up, preventing cold air distribution.

Question 4

If a compressor's internal overload protects it from overheating but the unit starts immediately after being reset manually, what concern exists?

Accepted Answer

The underlying cause of overheating was not corrected and the compressor will trip again

Answer

Resetting an overload without diagnosing and correcting the root cause (e.g., low refrigerant, dirty coils, high ambient) will result in repeated tripping.

Question 5

What is the purpose of the C (common) terminal on a 24V thermostat circuit?

Accepted Answer

It provides the return path for 24V AC from the transformer secondary

Answer

The C wire completes the 24V control circuit by returning current to the transformer's secondary common, allowing smart thermostats and other loads to operate continuously.

Air Conditioning Repair Practice Test

Air Conditioning Repair Practice Test

Air Conditioning Repair Electrical Components and Controls 4