HVAC Compressors and Condensing Units 1 — Questions and Answers
Question 1: What is the primary function of a compressor in a refrigeration cycle?
- Remove heat from the refrigerant
- Increase the pressure and temperature of the refrigerant vapor (Correct answer)
- Expand the refrigerant to lower its temperature
- Remove moisture from the refrigerant
Correct answer: Increase the pressure and temperature of the refrigerant vapor
The compressor raises the pressure of the low-pressure refrigerant vapor, which also raises its temperature so heat can be rejected in the condenser.
Question 2: Which type of compressor uses a piston moving back and forth inside a cylinder to compress refrigerant?
- Scroll compressor
- Centrifugal compressor
- Reciprocating compressor (Correct answer)
- Rotary compressor
Correct answer: Reciprocating compressor
A reciprocating compressor uses pistons driven by a crankshaft to compress refrigerant through back-and-forth (reciprocating) motion.
Question 3: What is the suction line in a refrigeration system?
- The line carrying high-pressure liquid from the condenser
- The line carrying low-pressure vapor from the evaporator to the compressor (Correct answer)
- The line carrying discharge gas to the condenser
- The line connecting the metering device to the evaporator
Correct answer: The line carrying low-pressure vapor from the evaporator to the compressor
The suction line carries low-pressure refrigerant vapor from the evaporator back to the compressor inlet.
Question 4: Which type of compressor uses two interlocking spiral-shaped scrolls to compress refrigerant?
- Reciprocating compressor
- Screw compressor
- Centrifugal compressor
- Scroll compressor (Correct answer)
Correct answer: Scroll compressor
A scroll compressor uses two interlocking spiral elements — one fixed and one orbiting — to trap and compress refrigerant.
Question 5: What does a high-pressure lockout on a condensing unit protect against?
- Low refrigerant charge
- Excessively high discharge pressure that could damage the compressor (Correct answer)
- Low ambient temperature operation
- Inadequate airflow across the evaporator coil
Correct answer: Excessively high discharge pressure that could damage the compressor
A high-pressure lockout switch shuts down the unit when discharge pressure exceeds safe limits, preventing compressor damage from excessive head pressure.
Question 6: What is 'liquid slugging' in a compressor?
- Refrigerant oil circulating through the system
- Liquid refrigerant entering the compressor and causing mechanical damage (Correct answer)
- A slow-running compressor due to low voltage
- Refrigerant migrating to the oil sump during the off cycle
Correct answer: Liquid refrigerant entering the compressor and causing mechanical damage
Liquid slugging occurs when liquid refrigerant enters the compressor, which cannot compress liquid and sustains serious mechanical damage as a result.
Question 7: On an air-cooled condensing unit, what is the purpose of the condenser fan?
- Draw return air across the evaporator coil
- Force outdoor air across the condenser coil to reject heat (Correct answer)
- Circulate refrigerant through the condenser
- Cool the compressor motor windings
Correct answer: Force outdoor air across the condenser coil to reject heat
The condenser fan moves ambient air over the condenser coil so the hot refrigerant vapor can reject its heat and condense into a liquid.
HVAC Compressors and Condensing Units 1
What is the primary function of a compressor in a refrigeration cycle?