Air Conditioning Repair Refrigeration System Repair 2 — Questions and Answers
Question 1: A technician measures suction pressure that is too high and discharge pressure that is too low. What is the most likely cause?
- Overcharged system
- Faulty compressor valves (Correct answer)
- Restricted liquid line
- Low refrigerant charge
Correct answer: Faulty compressor valves
Faulty compressor valves (worn or leaking) allow high-pressure gas to bypass back to the suction side, raising suction pressure and lowering discharge pressure.
Question 2: Which refrigerant is classified as an A2L (mildly flammable) and is commonly used as a replacement for R-22 in new equipment?
- R-410A
- R-32 (Correct answer)
- R-134a
- R-407C
Correct answer: R-32
R-32 is classified as A2L (mildly flammable) and is increasingly used in new equipment as an environmentally preferable alternative.
Question 3: When replacing a filter-drier on a refrigeration system, what is the correct procedure after installing the new drier?
- Immediately recharge the system
- Pull a deep vacuum before recharging (Correct answer)
- Pressurize with nitrogen to check for leaks only
- Flush the system with refrigerant before evacuating
Correct answer: Pull a deep vacuum before recharging
After replacing a filter-drier, a deep vacuum must be pulled to remove air and moisture before recharging with refrigerant.
Question 4: A refrigerant sight glass shows bubbles even though the system appears to have adequate charge. What could cause this besides low charge?
- Overcharged system
- High ambient temperature
- Pressure drop across a restriction in the liquid line (Correct answer)
- Condenser fan running too fast
Correct answer: Pressure drop across a restriction in the liquid line
A restriction in the liquid line causes a pressure drop that can flash refrigerant into vapor, producing bubbles in the sight glass even with sufficient charge.
Question 5: What is the purpose of a suction line accumulator in a refrigeration system?
- Store extra refrigerant charge
- Prevent liquid refrigerant from entering the compressor (Correct answer)
- Remove moisture from the refrigerant
- Separate oil from the refrigerant
Correct answer: Prevent liquid refrigerant from entering the compressor
A suction line accumulator catches any liquid refrigerant before it can reach the compressor, protecting it from liquid slugging damage.
Question 6: A technician finds the compressor running but no cooling occurring and the refrigerant charge appears correct. The metering device is a TXV. What should be checked first?
- Condenser coil cleanliness
- TXV bulb contact and charge (Correct answer)
- Evaporator fan motor
- Liquid line size
Correct answer: TXV bulb contact and charge
A TXV with a lost bulb charge or poor bulb contact will stay closed, preventing refrigerant flow and causing a no-cooling condition.
Question 7: Which condition would cause a refrigeration system to short-cycle (compressor turns on and off rapidly)?
- Oversized metering device
- Low refrigerant charge tripping the low-pressure switch (Correct answer)
- Dirty air filter on the return
- High discharge superheat
Correct answer: Low refrigerant charge tripping the low-pressure switch
A low refrigerant charge causes suction pressure to drop below the low-pressure switch cutout, cycling the compressor off, then on again repeatedly.
Air Conditioning Repair Refrigeration System Repair 2
A technician measures suction pressure that is too high and discharge pressure that is too low.
What is the most likely cause?