Compressor HVAC: Description and Operation

With the Ignition Switch (X134) in position 1, battery voltage is applied to the Heater And A/C Load Relay (K124). The relay is energized, applying battery voltage to the [1][2]Compressor Clutch Relay (K108) and Fan Speed Switch (X179). When the Fan Speed Switch is not in position 0 (off), battery voltage is supplied to the Air Supply Selector Switch (X180). When the selector switch is in the A/C And Heat Mode or in the A/C Mode, battery voltage is sent through the A/C Diode Pack (Z101) to the A/C Thermostat Unit (Z102), signaling the Thermostat Unit that compressor operation has been requested. The Thermostat Unit then applies battery voltage to the Engine Control Module (Z132) through the A/C Dual Pressure and Engine Temperature Switches (X102). The ECM then applies ground to the Compressor Clutch Relay coil. The relay energizes, applying battery voltage to the Compressor Clutch (K107).

If the A/C Dual Pressure Switch senses high or low pressure it opens. Battery voltage is removed from the ECM, which then removes ground from the [1][2]Compressor Clutch Relay, disengaging the Compressor Clutch.

The Thermostat Unit receives a temperature control signal from the Temperature Selector Control (X183) and a temperature input signal from the A/C Evaporator Temperature Sensor (X101). The Thermostat Unit uses these inputs to determine how often to signal the Engine Control Module (ECM) to cycle the Compressor Clutch.