A/C Compressor Cycling

The evaporator discharge air temperature sensor is an input to the BCM and is relayed to the PCM over the High Speed Controller Area Network (HS-CAN). The evaporator discharge air temperature sensor prevents icing of the evaporator by measuring the temperature of the airflow immediately after the evaporator. An accurate evaporator temperature is critical for compressor engagement. The PCM uses the temperature measurement to regulate the on and off time of the A/C compressor to maintain the evaporator temperature within an acceptable temperature range.

The PCM monitors the discharge pressure measured by the A/C pressure transducer. The PCM interrupts A/C compressor operation in the event the A/C pressure transducer indicates high system discharge pressures. It is also used to sense low charge conditions. If the pressure is below a predetermined value for a given ambient temperature, the PCM does not allow the A/C clutch to engage.