Electrical Components and Controls Flashcards
7 cards from real Air Conditioning Repair practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Electrical Components and Controls flashcards as text
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?
Answer: Low voltage from the transformer secondary
Insufficient transformer output or excessive voltage drop in the 24V control circuit causes low coil voltage, preventing the contactor from pulling in fully.
What is the purpose of a run capacitor in a single-phase PSC compressor motor?
Answer: To maintain a phase shift that improves running efficiency
A run capacitor stays in the circuit continuously, maintaining the phase shift between run and start windings to improve motor efficiency and power factor.
A dual-run capacitor is labeled 40/5 MFD 440V. Which terminal pair connects to the compressor?
Answer: HERM and C
The HERM (hermetic) terminal and C (common) terminal form the 40 MFD section used for the compressor motor.
Which safety device opens on a rise in discharge pressure and automatically resets when pressure drops?
Answer: High-pressure switch (auto-reset)
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.
A technician measures 240V across a contactor's load-side terminals with the contactor pulled in. What does this indicate?
Answer: Open contacts with load disconnected
Voltage across open load-side terminals indicates the contactor is not closing; if the contacts were closed, voltage would be near zero across them.
What happens to a start capacitor if it remains in the circuit longer than a few seconds?
Answer: It overheats and can fail or explode
Start capacitors are designed for short-duration use only; prolonged energization causes excessive heat buildup leading to failure.
A potential relay used in a hard-start kit opens its contacts when which condition is met?
Answer: Back-EMF across the start winding reaches approximately 75% of line voltage
The potential relay monitors the voltage induced in the start winding; once back-EMF rises to the relay's pick-up voltage, it opens to remove the start capacitor from the circuit.