Diagnostic Table
- Refer to HIGH AND LOW PRESSURE TABLE
.HIGH AND LOW PRESSURE TABLE
High (Discharge) Pressure Low (Suction) Pressure Component - Causes High or clutch cycling High Condenser - inadequate airflow. High Normal to high Engine overheating. Normal to high Normal Refrigerant overcharge - air in refrigerant. Normal to low High Thermostatic expansion valve sticking. Normal to low Normal to high A/C suction line - partially restricted or plugged(1). Normal to Low Low or clutch cycling Low refrigerant charge, A/C suction line - partially restricted or plugged(2). A/C cycling switch - sticking closed. Erratic operation or compressor not running A/C cycling switch. Poor connection at A/C clutch connector or clutch cycling switch connector. A/C electrical circuit erratic - see COMPONENT TESTING . Normal to low High Compressor - low performance. Additional Possible Cause Components Associated With Inadequate Compressor Operation - Compressor drive belt - loose
- Compressor clutch - slipping
- Clutch coil open - shorted, or loose mounting
- Control assembly switch - dirty contacts or sticking open
- Clutch wiring circuit - high resistance, open or blown fuse
- Compressor operation interrupted by engine computer
Additional Possible Cause Components Associated With a Damaged Compressor - Incorrect clutch air-gap
- Suction accumulator - refrigerant oil bleed hose plugged
- Refrigerant leaks
(1) Low pressure reading will be normal to high if pressure is taken at accumulator and if restriction is downstream of service access valve. (2) Low pressure reading will be low if pressure is taken near the compressor and restriction is upstream of service access valve.
NOTE:
The HIGH AND LOW PRESSURE TABLE
is used to guide diagnosis of the refrigerant system if operating pressures are outside normal limits.