General Information

The purpose of the Air Conditioning (A/C) system is to provide cool air and remove humidity from the interior of the vehicle. The vehicle operator can activate the A/C system by pressing the A/C switch. The A/C system can operate regardless of the temperature setting, however, recirculation is only available when the HVAC control module is in any mode other than FRONT DEFROST and MIX-BLEND.

The Powertrain Control Module (PCM) will operate the A/C system automatically. The PCM will command on the A/C compressor clutch to help reduce moisture inside the vehicle. The A/C compressor is on in selected modes, even in cool weather conditions, to help eliminate moisture from fogging the windshield. The A/C LED will not illuminate unless the driver presses the A/C request switch on the HVAC control module. Otherwise, the A/C system may be running without the A/C LED indicator illuminated.

Regardless of the selected A/C mode setting, a request is made to the Body Control System (BCM) to turn on the A/C compressor. The request is made by the HVAC control module to the BCM through the A/C request signal circuit when the BCM grounds the signal from the HVAC control module. The BCM then sends a class 2 message to the PCM on the ECM/BCM/VCM class 2 serial data circuit. The PCM grounds the A/C clutch relay control circuit and engages the A/C compressor clutch. Power is provided to the HVAC control module by the left IP junction block. Ground is provided by the ground circuit.

The PCM turns on the 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 from the engine junction block and ignition 1 voltage circuit. Once the relay closes its internal switch, power from the battery positive voltage circuit is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit. Whenever the compressor is turned off, the A/C compressor clutch diode prevents a voltage spike from burning up the compressor clutch coil. 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. The PCM will engage the A/C clutch any time the engine speed is below 5000 RPMs and the A/C is requested unless any of the following conditions exists:
^ Throttle angle is at 100 percent
^ The refrigerant pressure sensor has a low pressure condition 186 kPa (27 PSI) or lower
^ The refrigerant pressure sensor has a high pressure condition 2979 kPa (219 PSI) or higher
^ Engine Coolant Temperature (ECT) above 121°C (250°F)