A/C Request

When an A/C request is received by the PCM, the PCM engages the A/C clutch relay when all of the following conditions are met:

The PCM does not detect excessively high or low refrigerant pressure from the A/C pressure transducer.
The PCM does not detect an ambient air temperature below approximately 0°C (32°F).
The PCM does not detect temperatures from the Mass Airflow/Intake Air Temperature sensor that does not correlate with other temperature sensor readings at ignition ON. (Most Mass Airflow (MAF) sensors have an integrated Intake Air Temperature (IAT) sensor).
The PCM does not receive a message from the FCIM detecting an evaporator temperature below approximately 1°C (33.8°F).

The PCM monitors multiple temperature sensors correlation AAT, CACT, CHT, ECT, IAT, IAT2, MAF, MAPT, TCB and TCIPT (as applicable). The PCM runs this logic after an engine off and a calibrated soak period, typically 6 to 8 hours. This soak period allows the Ambient Air Temperature (AAT) sensor and the other temperature sensors to stabilize and not differ by greater than a calibrated value, typically 18°C (32.4°F). If a sensor input is found to be reporting a temperature imbalance the PCM does not allow the A/C clutch to engage. For more information on PCM sensors, Refer to the appropriate Engine Controls article.

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.

The FCIM may adjust the air inlet door depending on the humidity measured by the in-vehicle temperature and humidity sensor.