Air Conditioning (A/C) Compressor Control

The Air Conditioning (A/C) compressor incorporates both a conventional A/C clutch and an integral internal solenoid. The clutch and the solenoid are supplied with a current from the ATCM by a direct hardwired connection. By increasing the supply current of the solenoid, the internal stroke of the compressor is increased, which results in more refrigerant being pumped around the A/C system, which in turn lowers the evaporator temperature. Reducing the solenoid supply current results in the evaporator temperature rising.

When A/C is selected the ATCM maintains the evaporator at a target temperature that varies with the passenger compartment cooling requirements. If the requirement for cooled air decreases, the ATCM raises the evaporator operating temperature by reducing the flow of refrigerant provided by the A/C compressor. The ATCM closely controls the rate of temperature increase to avoid introducing moisture into the passenger compartment.

If the requirement for cooled air increases, the ATCM lowers the evaporator operating temperature by increasing the flow of refrigerant provided by the A/C compressor.

When A/C is selected off by pressing the A/C switch on the ICP, the compressor current signal supplied by the ATCM reduces the A/C compressor solenoid valve to the minimum flow position. The compressor clutch is then released and the compressor stops.

The ATCM incorporates limits for the operating pressure of the refrigerant system. When the system approaches the high pressure limit the compressor current signal is progressively reduced until the system pressure decreases. However, if the operating pressure continues to raise the compressor clutch is released and not allowed to re-engage until the pressure has dropped below a safe limit.