HVAC Refrigeration 2 — Questions and Answers
Question 1: What is the purpose of a thermostatic expansion valve (TXV) in a refrigeration system?
- Compress the refrigerant to high pressure
- Meter refrigerant flow to maintain superheat at the evaporator outlet (Correct answer)
- Remove heat from the condenser
- Separate liquid from vapor refrigerant
Correct answer: Meter refrigerant flow to maintain superheat at the evaporator outlet
A TXV meters refrigerant flow into the evaporator to maintain a set superheat, ensuring only vapor enters the compressor.
Question 2: What does 'subcooling' refer to in a refrigeration system?
- Cooling the suction line below ambient temperature
- Cooling liquid refrigerant below its condensing temperature at a given pressure (Correct answer)
- The process of cooling the compressor oil
- Reducing evaporator temperature below the setpoint
Correct answer: Cooling liquid refrigerant below its condensing temperature at a given pressure
Subcooling is the process of cooling liquid refrigerant below its saturation temperature at the condenser pressure, preventing flash gas in the liquid line.
Question 3: In a refrigeration cycle, where does the refrigerant absorb heat from the space being cooled?
- Condenser
- Compressor
- Evaporator (Correct answer)
- Expansion valve
Correct answer: Evaporator
The evaporator absorbs heat from the refrigerated space as liquid refrigerant evaporates into vapor.
Question 4: What refrigerant replaced R-22 as the most common choice for residential air conditioning in the US?
- R-134a
- R-404A
- R-410A (Correct answer)
- R-507
Correct answer: R-410A
R-410A replaced R-22 in residential AC systems because it has zero ozone depletion potential and higher efficiency.
Question 5: What is the function of a liquid line filter-drier in a refrigeration system?
- Increase refrigerant velocity in the liquid line
- Remove moisture and contaminants from the refrigerant (Correct answer)
- Subcool the refrigerant before the expansion device
- Separate oil from the refrigerant
Correct answer: Remove moisture and contaminants from the refrigerant
A filter-drier removes moisture and solid contaminants from the liquid refrigerant to prevent system damage and acid formation.
Question 6: What is 'flash gas' in a refrigeration system?
- Gas that escapes from the compressor during startup
- Refrigerant vapor that forms in the liquid line due to pressure drop or heat gain (Correct answer)
- The initial burst of hot gas discharged by the compressor
- Refrigerant that flashes to vapor inside the compressor
Correct answer: Refrigerant vapor that forms in the liquid line due to pressure drop or heat gain
Flash gas is unwanted refrigerant vapor that forms in the liquid line before the expansion device, reducing system efficiency.
Question 7: Which type of compressor uses rotating scrolls to compress refrigerant and is commonly found in modern residential heat pumps?
- Reciprocating compressor
- Screw compressor
- Scroll compressor (Correct answer)
- Centrifugal compressor
Correct answer: Scroll compressor
Scroll compressors use two interlocking spiral-shaped scrolls to compress refrigerant and are valued for their efficiency, quiet operation, and reliability in residential systems.
HVAC Refrigeration 2
What is the purpose of a thermostatic expansion valve (TXV) in a refrigeration system?