Air Conditioning Repair Car Air Conditioning Repair 4 — Questions and Answers
Question 1: Which electrical component engages and disengages the AC compressor on most conventional systems?
- Pressure relief valve
- Electromagnetic clutch (Correct answer)
- Blower motor relay
- Thermostatic switch
Correct answer: Electromagnetic clutch
The electromagnetic clutch magnetically couples the compressor pulley to the compressor shaft when energized, allowing the compressor to be driven by the serpentine belt only when needed.
Question 2: A manifold gauge shows high-side pressure of 350 psi and low-side pressure of 10 psi on a hot day. What does this pattern suggest?
- Overcharged system
- Blocked orifice tube or expansion valve (Correct answer)
- Failed condenser fan
- Normal operation
Correct answer: Blocked orifice tube or expansion valve
Extremely high discharge pressure combined with very low suction pressure is a classic sign of a restriction (blockage) in the metering device, starving the evaporator of refrigerant.
Question 3: What is the correct procedure for adding refrigerant to a car AC system that is slightly low?
- Add refrigerant to the high-side port with the engine off
- Add refrigerant as a liquid to the low-side port with the engine running and AC on (Correct answer)
- Add refrigerant as a gas to the high-side port with the engine running
- Add refrigerant to either port until pressures equalize
Correct answer: Add refrigerant as a liquid to the low-side port with the engine running and AC on
Refrigerant is added as a gas (or low-pressure liquid from an inverted can) to the low-side service port with the engine running and AC on max, never to the high side.
Question 4: What is a common symptom of a failed or slipping AC compressor clutch?
- AC blows cold then hot in cycles
- AC does not cool at all and compressor pulley spins freely without engaging the hub (Correct answer)
- Squealing noise from the blower motor
- High-side pressure reads zero
Correct answer: AC does not cool at all and compressor pulley spins freely without engaging the hub
A failed clutch coil or worn friction disc allows the pulley to spin without driving the compressor, so the system produces no pressure differential and no cooling.
Question 5: How does an orifice tube system differ from a TXV system in refrigerant metering?
- An orifice tube actively adjusts flow based on temperature; a TXV is fixed
- An orifice tube is a fixed restriction; a TXV dynamically modulates flow based on superheat (Correct answer)
- Both are identical in function but differ only in location
- A TXV is used only on electric vehicles
Correct answer: An orifice tube is a fixed restriction; a TXV dynamically modulates flow based on superheat
The orifice tube is a simple fixed-diameter metering device, while the TXV continuously adjusts refrigerant flow to maintain a set superheat at the evaporator outlet.
Question 6: After recharging, a technician notices the AC vent temperature is warmer than expected despite correct refrigerant charge. What component should be inspected next?
- Blower motor speed resistor
- Blend door actuator
- Condenser fins for dirt and blockage (Correct answer)
- High-pressure switch
Correct answer: Condenser fins for dirt and blockage
A clogged or bent condenser prevents adequate heat rejection, raising refrigerant temperature and reducing the system's ability to produce cold air even with a proper charge.
Question 7: What is the role of the AC pressure cycling switch found in some orifice tube systems?
- It limits blower motor speed at high pressure
- It cycles the compressor on and off to prevent evaporator freeze-up (Correct answer)
- It opens the high-side relief valve under overpressure
- It controls the condenser fan speed
Correct answer: It cycles the compressor on and off to prevent evaporator freeze-up
The pressure cycling switch monitors low-side pressure and cuts the compressor when pressure drops to the freeze point, then restarts it once pressure rises, regulating evaporator temperature.
Air Conditioning Repair Car Air Conditioning Repair 4
Which electrical component engages and disengages the AC compressor on most conventional systems?