ASE G1 Auto Maintenance and Light RepairHeating and Air Conditioning (HVAC)Medium
A technician is diagnosing an automotive HVAC system that produces warm air from the vents, despite the compressor engaging and the system having a full refrigerant charge. The high-side pressure is unusually low, and the low-side pressure is unusually high. Which of the following is the MOST likely cause?
- AA restricted expansion valve
- BAn overcharged system
- CA faulty condenser fan
- DAn inoperative compressor
Show answer & explanationAnswer & explanation
Correct answer: A. A restricted expansion valve
A restricted expansion valve prevents the proper flow of refrigerant into the evaporator, causing high pressure on the low side and low pressure on the high side as the compressor struggles to move refrigerant through the restriction.
Why the other options are wrong
- B. An overcharged system would result in excessively high pressures on both the high and low sides.
- C. A faulty condenser fan would lead to excessively high high-side pressure, not low high-side pressure.
- D. An inoperative compressor would result in pressures equalizing to ambient temperature, and the compressor would not be engaging.
Expansion Valve Restriction
A blockage or malfunction within the expansion valve that impedes the flow of refrigerant into the evaporator, significantly impacting AC system performance.
- Causes high low-side pressure and low high-side pressure.
- Results in poor or no cooling.
- Can be identified by temperature differences across the valve.
Memory trick: Pressure Puzzles Pinpoint Problems.