Electrical Systems 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 Systems and Controls flashcards as text
A hard start kit (potential relay and start capacitor) is added to a compressor. What is the primary purpose of this kit?
Answer: Increase starting torque to overcome high head pressure
A hard start kit boosts starting torque, allowing the compressor to start against elevated head pressure or under low-voltage conditions.
On a heat pump system, the reversing valve solenoid is energized in cooling mode. If the solenoid coil reads infinite resistance, what will happen?
Answer: The system will operate in heating mode only
An open reversing valve solenoid coil means the valve cannot be electrically shifted, leaving it in its de-energized (heating) position.
What is the purpose of a time-delay relay (TDR) installed in an air conditioning control circuit?
Answer: Prevent short cycling of the compressor by enforcing a minimum off time
A time-delay relay enforces a minimum off period between compressor cycles to protect against refrigerant pressure equalization issues and motor overheating.
A technician uses a megohmmeter to test a compressor motor winding to ground. A reading of 2 megohms is obtained. What does this indicate?
Answer: Moisture or degraded insulation is present
A compressor winding-to-ground reading below 1,000 megohms suggests compromised insulation, likely from moisture ingress or winding breakdown.
Which safety control opens the circuit to the compressor contactor coil when refrigerant pressure exceeds the set point?
Answer: High-pressure switch
The high-pressure switch is a normally closed safety device that opens to cut power to the contactor coil when discharge pressure exceeds its cut-out setting.
A technician finds that the outdoor unit is not running but the indoor blower is operating. The thermostat is calling for cooling. What sequence of checks is most efficient?
Answer: Check 24V at contactor coil, verify contactor pulls in, check 240V at compressor terminals
Starting with 24V at the coil, verifying contactor operation, then checking 240V at the load terminals follows a logical voltage-first diagnostic sequence.
What is the function of the 'Y' terminal on a standard residential thermostat?
Answer: Signals the cooling system compressor to run
The Y terminal sends the 24V cooling call signal to energize the contactor coil and start the compressor.