RSES Refrigeration Fundamentals & System Components 3 — Questions and Answers
Question 1: What condition is indicated when the suction pressure is lower than normal and the discharge pressure is also lower than normal?
- Refrigerant overcharge
- Refrigerant undercharge or low suction load (Correct answer)
- Condenser fouling
- Compressor valve failure
Correct answer: Refrigerant undercharge or low suction load
Low suction and low discharge pressures together typically indicate a refrigerant undercharge or insufficient heat load on the evaporator.
Question 2: In a hermetic compressor, the motor and compressor are:
- Separately driven through a belt drive
- Enclosed in the same sealed housing sharing refrigerant (Correct answer)
- Connected by a flexible coupling in an open housing
- Cooled by external water jackets only
Correct answer: Enclosed in the same sealed housing sharing refrigerant
A hermetic compressor seals both motor and compressor in one welded shell, with suction gas cooling the motor windings.
Question 3: The coefficient of performance (COP) of a refrigeration system is calculated as:
- Work input divided by heat rejected at the condenser
- Refrigerating effect divided by work input to the compressor (Correct answer)
- Condenser heat divided by evaporator heat
- Compressor power divided by system capacity
Correct answer: Refrigerating effect divided by work input to the compressor
COP = Q_evaporator / W_compressor, expressing how many units of heat are moved per unit of energy consumed.
Question 4: Which refrigerant is classified as an HFC (hydrofluorocarbon) with zero ozone depletion potential?
- R-22
- R-134a (Correct answer)
- R-11
- R-502
Correct answer: R-134a
R-134a is an HFC containing no chlorine, giving it zero ozone depletion potential (ODP), unlike older CFC and HCFC refrigerants.
Question 5: An oil separator in a refrigeration system is located:
- Between the evaporator and compressor
- Between the compressor and condenser (Correct answer)
- Between the condenser and expansion device
- Between the expansion device and evaporator
Correct answer: Between the compressor and condenser
Oil separators are installed in the discharge line to capture oil carried over from the compressor before it reaches the condenser and evaporator.
Question 6: What is the purpose of a sight glass installed in the liquid line?
- Measure refrigerant pressure
- Indicate refrigerant charge level and moisture presence (Correct answer)
- Control refrigerant flow rate
- Separate oil from refrigerant
Correct answer: Indicate refrigerant charge level and moisture presence
A sight glass allows technicians to observe bubbles (indicating low charge or flash gas) and a moisture indicator changes color if moisture is present.
Question 7: Sensible heat transfer in a refrigeration system occurs when:
- Refrigerant changes phase from liquid to vapor
- Temperature of a substance changes without a phase change (Correct answer)
- Refrigerant condenses from vapor to liquid
- Latent heat is absorbed in the evaporator
Correct answer: Temperature of a substance changes without a phase change
Sensible heat transfer changes the temperature of a substance without a phase change, unlike latent heat which involves phase changes at constant temperature.
RSES Refrigeration Fundamentals & System Components 3
What condition is indicated when the suction pressure is lower than normal and the discharge pressure is also lower than normal?