Compressor HVAC: Description and Operation

A/C COMPRESSOR
A/C systems on vehicles equipped with the 2.4L and 3.7L gasoline engines use a Sanden SD-7, reciprocating swash plate-type A/C compressor. This A/C compressor has a fixed displacement of 160 cubic centimeters (9.375 cubic inches) and includes an integral high pressure relief valve.

A/C systems on vehicles equipped with the 2.8L diesel engine use a Sanden PXF-18, reciprocating wobble plate-type A/C compressor. This A/C compressor has a fixed displacement of 150 cubic centimeters (9.763 cubic inches).

Both A/C compressors have the suction and discharge ports located on the compressor cylinder head and have a label identifying the use of R-134a refrigerant.

The A/C compressor is driven by the engine through an electric clutch, drive pulley and belt arrangement. The A/C compressor is lubricated by refrigerant oil that is circulated throughout the refrigerant system with the refrigerant.

The A/C compressor draws in low-pressure refrigerant vapor from the A/C evaporator through its suction port. It then compresses the refrigerant into a high-pressure, high-temperature refrigerant vapor, which is then pumped to the A/C condenser through the compressor discharge port.

The A/C compressor cannot be repaired and, if faulty or damaged, it must be replaced. The compressor clutch, pulley and bearing assembly, and clutch field coil are available for service.

HIGH PRESSURE RELIEF VALVE
A high pressure relief valve is located on the cylinder head of the Sanden SD-7 A/C compressor, which is at the rear of the compressor. This mechanical valve is designed to vent refrigerant from the A/C system to protect against damage to the A/C compressor and other A/C system components, caused by condenser air flow restriction or an overcharge of refrigerant.

The high pressure relief valve vents refrigerant from the A/C system when a discharge pressure of 3445 to 4135 kPa (500 to 600 psi) or above is reached. The high pressure relief valve closes with a minimum discharge pressure of 2756 kPa (400 psi) is reached.

The high pressure relief valve vents only enough refrigerant to reduce the A/C system pressure, and then re-seats itself. The majority of the refrigerant is conserved in the A/C system. If the high pressure relief valve vents refrigerant, it does not mean the valve is faulty.

The high pressure relief valve is factory-calibrated and cannot be adjusted or repaired, and must not be removed or otherwise disturbed. The valve is only serviced as a part of the A/C compressor.