CFESA Refrigeration Systems 2 — Questions and Answers
Question 1: Subcooling in a refrigeration system refers to:
- Cooling the suction line below ambient
- Cooling liquid refrigerant below its condensing temperature (Correct answer)
- Operating the evaporator below freezing
- Reducing compressor discharge temperature
Correct answer: Cooling liquid refrigerant below its condensing temperature
Subcooling ensures the liquid refrigerant is cooled below its condensing temperature, preventing flash gas before the expansion device.
Question 2: Which type of expansion device maintains a constant evaporator pressure regardless of load?
- Thermostatic expansion valve (TXV)
- Automatic expansion valve (AXV) (Correct answer)
- Capillary tube
- Electronic expansion valve (EEV)
Correct answer: Automatic expansion valve (AXV)
The automatic expansion valve (AXV) maintains a constant evaporator pressure by responding to pressure changes at the valve outlet.
Question 3: What condition is indicated when a compressor's suction line frosts heavily all the way back to the compressor?
- Normal operating condition
- Overcharge of refrigerant or a flooding TXV (Correct answer)
- Low refrigerant charge
- High ambient temperature
Correct answer: Overcharge of refrigerant or a flooding TXV
Heavy frosting on the suction line extending to the compressor indicates liquid refrigerant is returning to the compressor, risking liquid slugging.
Question 4: In a commercial refrigeration system, what is the role of the oil separator?
- Filter moisture from the oil
- Return compressor oil from the discharge line back to the crankcase (Correct answer)
- Separate refrigerant from oil in the evaporator
- Prevent oil from entering the condenser
Correct answer: Return compressor oil from the discharge line back to the crankcase
The oil separator captures oil discharged with the hot gas and returns it to the compressor crankcase, preventing oil accumulation in the system.
Question 5: What is the typical evaporator temperature range for a commercial ice cream freezer (hardening cabinet)?
- -10°F to 0°F
- 0°F to 15°F
- -40°F to -20°F (Correct answer)
- 20°F to 35°F
Correct answer: -40°F to -20°F
Hardening cabinets require very low evaporator temperatures, typically -40°F to -20°F, to rapidly freeze and maintain ice cream at proper hardness.
Question 6: A technician notices oil pooling in the evaporator of a low-temperature display case. The most appropriate corrective action is:
- Add more refrigerant
- Check and increase the refrigerant charge
- Verify oil return lines and compressor crankcase heater operation (Correct answer)
- Replace the expansion valve
Correct answer: Verify oil return lines and compressor crankcase heater operation
Oil pooling in the evaporator indicates poor oil return; checking oil return lines and crankcase heater ensures oil circulates back to the compressor.
CFESA Refrigeration Systems 2
Subcooling in a refrigeration system refers to: