Creates pressure differential that drives refrigerant flow (The compressor increasses presure and the TXV drops it again). Increases refrigerant temperature and pressure for heat rejection at condenser.
Belt-driven from engine. Electromagnetic clutch engages when AC is activated. Internal pistons or scroll compress refrigerant vapor.
Pumps ship with oil -capacity of entire system.
Mounted on engine block or accessory bracket. Driven by serpentine belt. Look for electrical connector and refrigerant lines. Access varies by model series.
Pulley free-wheels when disengaged. When energized, clutch plate engages and drives compressor shaft. CLutch runs at about 3 amps. Use your high-current test light to supstitute test.
Suction line (low side): Larger, insulated, cold. Discharge line (high side): Smaller, hot to touch. Check for oil residue indicating leaks.
Key on, engine off. Turn AC on. After 6-second MCC delay, clutch should engage with audible click. If no click, substitute test using your high-current test light. By-pass AC pressure switch.
Discharge line should be very hot (near engine temp). Suction line should be cold (It's OK for it to be sweating and frosted). Large temperature difference indicates proper compression.
Check belt condition, oil leaks, loose mounting bolts. Listen for unusual noises during operation.
Use high-current test light to substitute clutch. During operation, check system for 8x pressure differential.
Compressor failures often result from lack of oil, improper oil, or contamination. Use the correct oil type and quantity. The oil is circulated by the refrigerant. Don't operate a compressor without enough refrigerant in the system.
| Symptom | Cause | Diagnosis |
|---|---|---|
| Clutch not engaging | Low/High pressure, Electrical fault | Bypass pressure switch. Check MCC codes. Substitute test clutch. |
| Loud grinding noise | Internal bearing failure, piston damage, broken reed valves | Check for metal in system. Inspect system oil. |
| No compression | Internal seal failure, broken reed valves, damaged pistons | Not able to build the 8x pressure difference, no temperature difference across compressor |
| Oil leak | Failed shaft seal, loose fittings, cracked housing | Visual inspection, oil residue around compressor shaft and fittings |
| Clutch slipping | Worn clutch plate, incorrect air gap, weak coil | Clutch engages but doesn't drive compressor, burning smell |
Compressor replacement requires complete system flush. Failed compressor can send metal debris throughout system. Always replace receiver/dryer, condenser, TXV, and evaporator. Flush the lines.
When charging through the low (suction) side, add refrigerant as a vapor — never liquid. Compressors are designed to compress vapor; liquid refrigerant does not compress. Liquid slugging the compressor can hydrolock and shatter reed valves, bend connecting rods, or blow out the head on the first stroke. When using the compressor to pull refrigerant into the system, always charge from the top of an upright cylinder/can (or use a can tap set to vapor position) with the engine and compressor running, and add refrigerant slowly while monitoring system pressures.