A/C Relay and Clutch Controls

The A/C compressor clutch is controlled by the Powertrain Control Module (PCM). This allows the PCM to manage idle quality, improve Wide Open Throttle (WOT) performance, and protect the A/C system from excessively high and low pressures.

The PCM controlled air conditioning system uses a variable displacement compressor. The compressor meets the A/C requirements without cycling.

Operation
The PCM controlled air conditioning system consists of an A/C relay, an A/C clutch and an A/C refrigerant pressure sensor. The BCM and A/C request switch also input the PCM through serial data circuit.

The A/C refrigerant pressure sensor is used to indicate high side pressures. The PCM uses this information to control: the cooling fan operation, the A/C clutch operation and idle speed. A fault in the A/C refrigerant pressure sensor circuit will set a DTC P0530. This will cause the PCM to disable the A/C clutch.

The PCM determines high and low pressures in the A/C system by the voltage signal it receives from the A/C refrigerant pressure sensor. This allows the PCM to protect the A/C system from excessively high and low pressures. If the A/C refrigerant pressure sensor exceeds 435 psi the PCM will disable the A/C clutch. The A/C clutch will remain disabled until the A/C refrigerant pressure sensor voltage falls about 290 psi.

The PCM will temporarily disable the A/C compressor clutch during the following conditions:
^ A wide open throttle.
^ A high rpm.
^ High power steering loads.
^ hot engine restarts.
^ If the engine coolant temperature exceeds 120°C (248°F).

The BCM contains the algorithm used for evaporator freeze protection. The BCM will send a class II message to turn the A/C clutch On/Off based on its calculations.