Air Conditioning Repair Car Air Conditioning Repair 3 — Questions and Answers
Question 1: Which refrigerant replaced R-12 in most automotive AC systems manufactured after 1994?
- R-22
- R-410A
- R-134a (Correct answer)
- R-1234yf
Correct answer: R-134a
R-134a became the standard automotive refrigerant after the EPA phased out ozone-depleting R-12 under the Clean Air Act, though newer vehicles use R-1234yf.
Question 2: A customer complains of a musty odor from the AC vents but normal cooling. What is the most likely cause?
- Refrigerant leak near the evaporator
- Mold or bacteria growth on the evaporator coil (Correct answer)
- Burned blower motor windings
- Contaminated compressor oil
Correct answer: Mold or bacteria growth on the evaporator coil
Moisture and organic debris on the evaporator surface create an ideal environment for mold and bacteria, producing a musty smell that enters the cabin through the vents.
Question 3: What does TXV stand for in an automotive AC system, and what is its function?
- Thermal Expansion Valve — meters refrigerant flow into the evaporator (Correct answer)
- Total Vent Exchange — controls cabin air circulation
- Turbo Exhaust Valve — manages backpressure
- Temperature eXchange Ventilator — regulates condenser temperature
Correct answer: Thermal Expansion Valve — meters refrigerant flow into the evaporator
The Thermal Expansion Valve (TXV) regulates the amount of refrigerant entering the evaporator based on evaporator outlet temperature, optimizing efficiency.
Question 4: Both high-side and low-side pressures are abnormally low on a running AC system. What does this most likely indicate?
- Restriction in the liquid line
- System is undercharged (low refrigerant) (Correct answer)
- Condenser fan failure
- Compressor valve failure
Correct answer: System is undercharged (low refrigerant)
When both pressures are uniformly low, the refrigerant charge is insufficient to maintain normal operating pressures on either side of the system.
Question 5: When replacing an AC compressor, why must a specific amount of oil be added to the new unit?
- To pre-lubricate seals before the first start
- To compensate for oil retained in old system components (Correct answer)
- To flush residual refrigerant from the lines
- To adjust the compressor displacement
Correct answer: To compensate for oil retained in old system components
Old system components (condenser, evaporator, lines) retain a portion of compressor oil, so the replacement compressor must be pre-filled to match total system oil capacity.
Question 6: A car AC condenser fan runs only when the AC is on. The engine is overheating in traffic. What is the likely fault?
- Blown AC fuse
- Engine coolant temperature sensor failed
- Condenser fan relay or control wiring not triggering the fan for engine cooling (Correct answer)
- Low refrigerant pressure
Correct answer: Condenser fan relay or control wiring not triggering the fan for engine cooling
The condenser fan should activate both for AC operation and independently when coolant temperature reaches a threshold; a relay or wiring fault can disable the cooling-mode trigger.
Question 7: What safety precaution must be taken when handling R-134a refrigerant in liquid form?
- Wear flame-resistant gloves
- Wear safety goggles and insulated gloves to prevent frostbite (Correct answer)
- Ground yourself to prevent static discharge
- Use a respirator rated for organic vapors
Correct answer: Wear safety goggles and insulated gloves to prevent frostbite
Liquid R-134a evaporates rapidly on contact with skin or eyes, causing severe frostbite and injury; PPE including goggles and thermal-insulating gloves is required.
Air Conditioning Repair Car Air Conditioning Repair 3
Which refrigerant replaced R-12 in most automotive AC systems manufactured after 1994?