Compressor HVAC: Description and Operation

A/C COMPRESSOR - GASOLINE ENGINES
The air conditioning system on vehicles equipped with a gasoline engine use a Sanden SD-7, reciprocating swash plate-type compressor. This compressor has a fixed displacement of 160 cubic centimeters and has both the suction and discharge ports located on the cylinder head. This compressor includes an integral high pressure relief valve. A label identifying the use of R-134a refrigerant is located on the compressor.

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

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

The compressor cannot be repaired. If faulty or damaged, the entire compressor assembly must be replaced. The compressor clutch, pulley and clutch coil are available for service.

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

The high pressure relief valve vents the system when a discharge pressure of 3445 to 4135 kPa (500 to 600 psi) or above is reached. The valve doses when a minimum discharge pressure of 2756 kPa (400 psi) is reached.

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

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