A/C Compressor Control

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

If the requirement for cooled air increases, the automatic temperature control (ATC) module lowers the evaporator operating temperature by increasing the flow of refrigerant provided by the air conditioning (A/C) compressor.

When air conditioning (A/C) is off, the compressor current signal supplied by the automatic temperature control (ATC) module holds the air conditioning (A/C) compressor solenoid valve in the minimum flow position, effectively switching off the air conditioning (A/C) function.

The automatic temperature control (ATC) module 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 air conditioning (A/C) compressor is maintained at its minimum stroke. This avoids depletion of the lubricant from the air conditioning (A/C) compressor.