Air Conditioning Repair Car Air Conditioning Repair 2 — Questions and Answers
Question 1: What tool is required to safely recover refrigerant from a car AC system before opening it for repair?
- Vacuum pump
- Refrigerant recovery machine (Correct answer)
- Manifold gauge set
- Nitrogen tank
Correct answer: Refrigerant recovery machine
A refrigerant recovery machine captures refrigerant from the system into a certified recovery cylinder, which is legally required before any AC repair that opens the system.
Question 2: A car's AC blows cold for 10 minutes then gradually turns warm. What is the most likely cause?
- Faulty compressor clutch
- Icing of the evaporator due to low refrigerant (Correct answer)
- Clogged cabin air filter
- Weak blower motor
Correct answer: Icing of the evaporator due to low refrigerant
Low refrigerant causes the evaporator coil to drop below freezing, forming ice that blocks airflow; once the ice melts, cooling briefly returns before icing again.
Question 3: Which component in a car AC system is responsible for removing moisture from the refrigerant?
- Expansion valve
- Condenser
- Receiver-drier (Correct answer)
- Evaporator
Correct answer: Receiver-drier
The receiver-drier contains desiccant material that absorbs moisture from the refrigerant, preventing ice formation and acid contamination.
Question 4: What does a high-side pressure reading significantly above normal indicate during AC diagnosis?
- Low refrigerant charge
- Restricted or failing condenser (Correct answer)
- Faulty expansion valve stuck open
- Compressor clutch slipping
Correct answer: Restricted or failing condenser
Abnormally high discharge-side pressure typically points to poor condenser airflow, a dirty condenser coil, or a failing condenser fan that prevents heat rejection.
Question 5: When leak-testing a car AC system after repair, which method is preferred for locating small leaks?
- Pressurize with refrigerant and use soapy water
- Pressurize with nitrogen and use an electronic leak detector
- Run the system and observe pressure drop
- Inject UV dye then use a UV lamp (Correct answer)
Correct answer: Inject UV dye then use a UV lamp
UV dye injection followed by UV lamp inspection is a precise, widely accepted method that visually highlights even small leak points without risk of contaminating a dry system.
Question 6: A technician finds the AC compressor cycling on and off rapidly (short cycling). What is the most likely cause?
- Overcharged system
- Low refrigerant triggering the low-pressure cutoff switch (Correct answer)
- Faulty blower motor resistor
- Clogged expansion valve
Correct answer: Low refrigerant triggering the low-pressure cutoff switch
Low refrigerant causes system pressure to drop below the low-pressure switch threshold, cutting the compressor off; it restarts once pressure rises slightly, causing rapid cycling.
Question 7: What is the purpose of pulling a vacuum (evacuation) on a car AC system before recharging?
- To test the compressor output
- To remove air and moisture from the system (Correct answer)
- To circulate UV dye throughout the lines
- To verify condenser fan operation
Correct answer: To remove air and moisture from the system
Evacuation lowers system pressure below atmospheric, boiling off any moisture and purging non-condensable air that would raise head pressure and reduce efficiency.
