Compressor HVAC: Description and Operation

With the ignition switch in ON (II), the climate control unit receives battery voltage through the BLK/YEL wire at cavity 2. The climate control unit is grounded by a BLK wire at G4O4.

When you push the A/C ON/OFF button with the ignition switch in ON (II), the climate control unit will ground the A/C ON input at cavity 3 of the Powertrain Control Module (PCM) through the A/C pressure switch.

The PCM grounds the A/C compressor clutch relay when the ignition switch is in ON (II). The clutch relay then energizes the compressor clutch, which engages and begins turning the compressor.

The climate control unit monitors the operation of the air conditioning system in the car through the in car temperature sensor, outside the car with the outside air temperature sensor, and in the evaporator outlet with the evaporator temperature sensor.

The climate control unit monitors the amount of direct sunlight in the car with the sunlight sensor, and monitors the Engine Coolant Temperature (ECT) with the ECT sensor in the heater/evaporator unit.

When refrigerant pressure becomes too high (due to blockage), or too low (due to leakage), the A/C pressure switch will open, disengaging the A/C compressor clutch.