Compressor HVAC: Description and Operation

CIRCUIT OPERATION
The Compressor for air conditioning is belt driven by the Engine. The A/C Compressor Clutch engages and disengages the Compressor to remove the air conditioning load from the Engine when needed. The A/C Compressor Control Clutch engages the Compressor when the A/C mode selector is in "MAX", "A/C", "BIL", "MIX" or "DEFROST."

The A/C Compressor Clutch Diode connected across the A/C Compressor Clutch suppresses high voltage spikes that are generated by the collapsing magnetic field of the clutch coil when the clutch is turned off.

The A/C Compressor Relay opens and closes the circuit to the A/C Compressor Clutch. The coil of the relay is grounded by the Engine Control Module (ECM). This enables the ECM to disengage the air conditioning to reduce the load on the Engine when required. Wide open throttle, high power steering pressure or coolant temperature will also prevent the A/C system from engaging.

The ECM receives an air conditioning "ON" signal, which is battery voltage from the HVAC Control Assembly. It signals the ECM that A/C Compressor operation is required. The ECM also monitors a signal voltage from the A/C Pressure Sensor. If either a low or high refrigerant pressure condition occurs, the ECM will prevent the A/C Compressor Clutch from engaging.