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 Engine Controls - Description & Operation (Except Diesel & Hybrid) .

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.