A/C Compressor Control

When A/C is selected the ATCM maintains the evaporator at an operating 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 off, the compressor current signal supplied by the ATCM holds the A/C compressor solenoid valve in the minimum flow position, effectively switching off the A/C function.

The ATCM incorporates limits for the operating pressure of the refrigerant system. If the system approaches the high pressure limit, the compressor current signal is progressively reduced until the system pressure decreases. If the system falls below the low pressure limit, the compressor current signal is held at its lowest setting so that the A/C compressor is maintained at its minimum stroke. This avoids depletion of the lubricant from the A/C compressor.