Compressor HVAC: Description and Operation
COMPRESSOR
The Saturn compressor is a variable displacement rotary vane type pump. The rotor assembly houses five lightweight vanes that extend outward contacting the cylinder wall creating the compression area. The compressor has an internal control valve that allows it to change its pumping capacity or displacement, reacting to heat loads on the air conditioning system. The range of displacement can vary from 5 percent (5.5 cc) to 100 percent (110 cc). The compressor's natural or resting state is at minimum displacement.
The compressor performs two main functions. It compresses the low pressure refrigerant vapor from the evaporator into a high pressure high temperature vapor, and pumps compressor oil through the A/C system.
COMPRESSOR CLUTCH
The electromagnetic clutch engages the compressor when the A/C button is depressed. The clutch consists of a drive plate, pulley, and a coil assembly. The drive plated is bolted to the compressor shaft. The pulley and bearing assembly is press fit onto the compressor hub, and the coil assembly is screwed to the compressor body. When current flows through the coil assembly, the drive plate is pulled into the pulley by electromagnetic force.
When the coil assembly is not energized the drive plate separates from the pulley and the compressor stops. A diode is used to protect electrical circuits from voltage spikes. The diode is located in the underhood junction block.
A thermal link fuse is incorporated into the coil. If the temperature of the coil exceeds 214°C ± 3°C (417°F ± 37°F), the link will melt creating an open coil circuit. When the coil is de-energized the drive plate releases the pulley and the compressor stops pumping. A typical coil resistance will measure 3.22 ± 0.08 ohms at 22°C (72°F).
PRESSURE RELIEF VALVE
Mounted in the front head is a high pressure relief valve. To protect the A/C system from high pressure in the event of an electrical control system failure the valve will begin to open at about 3654 kPa (530 psi). As system pressure is reduced the valve will reseat at about 2930 (425 psi). If the valve ever opens it must be replaced.