Air Conditioning Repair Electrical Components and Controls 2

Question 1

A contactor's coil is rated at 24V but the unit reads only 18V at the coil terminals during a call for cooling. What is the most likely cause?

Accepted Answer

Low voltage from the transformer secondary

Answer

Insufficient transformer output or excessive voltage drop in the 24V control circuit causes low coil voltage, preventing the contactor from pulling in fully.

Question 2

What is the purpose of a run capacitor in a single-phase PSC compressor motor?

Accepted Answer

To maintain a phase shift that improves running efficiency

Answer

A run capacitor stays in the circuit continuously, maintaining the phase shift between run and start windings to improve motor efficiency and power factor.

Question 3

A dual-run capacitor is labeled 40/5 MFD 440V. Which terminal pair connects to the compressor?

Accepted Answer

HERM and C

Answer

The HERM (hermetic) terminal and C (common) terminal form the 40 MFD section used for the compressor motor.

Question 4

Which safety device opens on a rise in discharge pressure and automatically resets when pressure drops?

Accepted Answer

High-pressure switch (auto-reset)

Answer

An auto-reset high-pressure switch opens the control circuit when discharge pressure exceeds its setpoint and closes again once pressure falls below the reset point.

Question 5

A technician measures 240V across a contactor's load-side terminals with the contactor pulled in. What does this indicate?

Accepted Answer

Open contacts with load disconnected

Answer

Voltage across open load-side terminals indicates the contactor is not closing; if the contacts were closed, voltage would be near zero across them.

Air Conditioning Repair Practice Test

Air Conditioning Repair Practice Test

Air Conditioning Repair Electrical Components and Controls 2