A/C Compressor Clutch Relay

The engine controller controls the A/C compressor clutch through a relay. This allows the engine controller to receive an A/C select signal when driver moves mode lever into A/C position. The engine controller also receives a request signal from the A/C temperature control thermostat (evaporator switch).

The engine controller then adjusts idle speed using the AIS motor. Only then can the engine controller activate the A/C compressor clutch through the A/C compressor clutch relay. The increased idle speed will compensate for the additional load caused by the A/C compressor.

On 4.0L engine, whenever the A/C compressor clutch is energized, the engine controller also energizes the radiator (cooling) fan relay. This occurs regardless on engine coolant temperature.