A/C Mode

The A/C system is activated by placing mode switch in any position and pressing the A/C switch. The A/C system operates regardless of temperature setting. The PCM will operate A/C system without any driver input. The PCM will command the A/C compressor clutch on to reduce moisture inside of vehicle. The A/C compressor is on, even in cool weather conditions, to keep moisture from fogging the windshield. The A/C LED will not illuminate unless the driver presses A/C switch on HVAC control module. The A/C system may be running without the A/C LED indicator being lit.

Regardless of selected A/C setting, a request is made to the PCM to turn on A/C compressor on the class 2 serial data circuit. The request is made by the HVAC control module to the Body Control Module (BCM) through the A/C request signal circuit when the A/C switch grounds the 12-volt signal from the BCM. The BCM then sends a class 2 message to the PCM on the BCM class 2 serial data circuit. The PCM grounds the clutch relay control circuit and engages the A/C compressor clutch.

The PCM turns on A/C compressor by providing a path to ground through the A/C clutch relay control circuit for the A/C compressor clutch relay. Power is provided to the A/C compressor clutch relay internally through the underhood junction block. Once the relay closes, battery voltage is provided to A/C compressor clutch through the A/C compressor clutch supply voltage circuit. Whenever A/C compressor is turned off, the A/C compressor clutch diode, located in the underhood junction block, prevents voltage spikes. The ground circuit provides a path to ground for the compressor and relay. The A/C clutch relay control circuit is grounded internally within the PCM.