Air Conditioning Repair Car Air Conditioning Repair 5 — Questions and Answers
Question 1: What does a bubbling or foamy sight glass indicate in a vehicle AC system that uses one?
- Normal operation at correct charge
- Low refrigerant charge (Correct answer)
- Overcharged system
- Moisture contamination
Correct answer: Low refrigerant charge
Bubbles or foam in the sight glass indicate that refrigerant is flashing to vapor in the liquid line due to insufficient charge, which reduces system efficiency.
Question 2: Which refrigerant is now required in new passenger vehicles sold in the US due to its lower global warming potential?
- R-134a
- R-22
- R-1234yf (Correct answer)
- R-410A
Correct answer: R-1234yf
R-1234yf has a global warming potential (GWP) of less than 1 compared to R-134a's GWP of 1,430, making it the mandated refrigerant for new US passenger cars.
Question 3: A technician measures superheat at the evaporator outlet and finds it excessively high. What does this indicate about the TXV?
- TXV is stuck open, flooding the evaporator
- TXV is stuck closed or restricted, starving the evaporator (Correct answer)
- System is overcharged
- Condenser is oversized
Correct answer: TXV is stuck closed or restricted, starving the evaporator
High superheat means refrigerant is fully evaporated well before the evaporator outlet, indicating insufficient refrigerant flow from a restricted or malfunctioning TXV.
Question 4: What is the primary reason an AC system should never be charged by weight alone without also checking operating pressures?
- Scale accuracy is insufficient for automotive work
- System restrictions or component failures won't show in weight but will affect pressures (Correct answer)
- Refrigerant weight varies with ambient temperature
- EPA regulations prohibit weight-based charging
Correct answer: System restrictions or component failures won't show in weight but will affect pressures
Charging by weight adds the correct amount of refrigerant but cannot detect restrictions, valve failures, or other issues that manifest only in abnormal pressure readings.
Question 5: When diagnosing an AC system, a technician finds both high-side and low-side pressures are too high. What is the most likely cause?
- Low refrigerant
- Expansion device stuck open or overcharged system (Correct answer)
- Faulty low-pressure switch
- Worn compressor
Correct answer: Expansion device stuck open or overcharged system
Uniformly elevated pressures on both sides indicate either an overcharge or an expansion device stuck open that allows too much refrigerant to flood the low side.
Question 6: What is the correct way to identify the high-side and low-side service ports on a car AC system?
- High-side port is larger; low-side port is smaller
- High-side port is on the compressor outlet/condenser side; low-side is on the evaporator outlet/compressor inlet side (Correct answer)
- High-side is always blue-labeled; low-side is always red-labeled
- They are interchangeable and identified only by pressure gauges
Correct answer: High-side port is on the compressor outlet/condenser side; low-side is on the evaporator outlet/compressor inlet side
The high-side service port is located between the compressor outlet and expansion device, while the low-side port is between the evaporator outlet and compressor inlet.
Question 7: A vehicle owner reports that the AC works fine in the morning but stops cooling when the outside temperature exceeds 95°F. What should be checked first?
- Refrigerant charge level and condenser airflow (Correct answer)
- Blower motor current draw
- Cabin air filter restriction
- Thermostat opening temperature
Correct answer: Refrigerant charge level and condenser airflow
High ambient temperatures stress the refrigerant system; a marginally low charge or partially blocked condenser that copes at mild temperatures will fail to reject enough heat when it is very hot outside.
Air Conditioning Repair Car Air Conditioning Repair 5
What does a bubbling or foamy sight glass indicate in a vehicle AC system that uses one?