With Electronic Climate Control

COMPRESSOR
The compressor for the air conditioning system is belt-driven by the engine. The A/C Compressor Clutch turns the compressor on and off. This controls the cooling and also removes the air conditioning load from the engine when needed. With the A/C Mode Selector in MAX, NORM, BI-LEVEL, or DEF, VENT, HTR, and with adequate refrigerant in the system, the Compressor Clutch will engage the compressor.

PRESSURE CYCLING SWITCH
The Pressure Cycling Switch turns the compressor off when the evaporator temperature is low enough to cause icing. The switch is located in the low pressure, or vapor side of the system. It opens when the refrigerant pressure is less than 172 kPa (25 psi). This opens the circuit to the A/C Compressor Clutch. This switch also closes to cycle the compressor on again when the evaporator temperature and pressure rise enough to require more cooling.

IDLE SPEED POWER STEERING PRESSURE SWITCH
The Idle Speed Power Steering Pressure Switch is normally closed. It opens to interrupt the voltage applied to the A/C Compressor Control Relay, turning off the compressor. This switch opens when heavy power steering loads are imposed, such as when parking the car.

COMPRESSOR CONTROL RELAY
The A/C Compressor Control Relay opens and closes the circuit to the A/C Compressor Clutch. The coil of the relay is grounded through the Electronic Control Module (ECM). This enables the ECM to control the compressor and turn off air conditioning to reduce the load on the engine when required. The ECM also receives an Air Conditioner On signal. This battery voltage from terminal B of the A/C Compressor Control Relay signals that the system has been turned on at the Heater and A/C Control Assembly and that the Pressure Cycling Switch is closed, indicating additional cooling is required.

A/C CLUTCH DIODE
Whenever the A/C Compressor Clutch is de-energized, large voltage spikes are generated across the terminals by the collapsing magnetic field. The A/C Clutch Diode provides a path for this voltage.