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 A/C system is engaged when the VENT switch is pressed or the HVAC control module is in FRONT DEFROST or MIX-BLEND mode. The A/C system can operate regardless of the temperature setting, as long as outside ambient temperature is above 4°C (40°F). If A/C is selected and A/C is not available, the VENT LED will light for one second and then go off, indicating that A/C is not allowed. The vehicle passenger can adjust the temperature offset by pressing the right air temperature switches. Passenger temperatures can be set 3°C (6°F) cooler or warmer than the primary setting. The HVAC control module receives power from the I/P fuse block on the ignition 3 voltage circuit along with the battery positive circuit. The module is grounded by the ground circuit. The HVAC control module communicates directly to the Powertrain Control Module (PCM) on the HVAC class 2 serial data circuit, through a splice pack, and through the ECM/PCM/VCM class 2 serial data circuit. Regardless of the selected A/C mode setting, a request is made to the PCM to turn on the A/C compressor. The request is made to the PCM from the HVAC control module through the HVAC class 2 serial data circuit, through a splice pack, and through the ECM/PCM/VCM class 2 serial data circuit. The PCM turns on the A/C compressor by providing a path to ground through the A/C compressor clutch relay control circuit for the A/C compressor clutch relay. Power is provided to the A/C compressor clutch relay internally of the underhood fuse block. Once the A/C compressor clutch relay closes its internal switch, power from the battery 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. The A/C clutch relay control circuit is grounded internally within the PCM.

The PCM will engage the A/C compressor clutch any time the engine speed is below 5000 RPM and the A/C is requested unless any of the following conditions exist:
^ Throttle angle is at 100 percent (WOT).
^ Vehicle launch, acceleration from a stop.
^ Idle quality
^ The A/C refrigerant pressure sensor is more than 2826 kPa (410 psi) or is less than 207 kPa (30 psi).
^ Engine speed is more than 5500 RPM.
^ Engine coolant temperature (ECT) is more than 124°C (255°F) for the LG8 and 121°C (250°F) for the L36.
^ Transmission shift
^ Engine torque load

For a description of the RPO Code(s) shown in this article/image, refer to the RPO Code List found at Vehicle/Application ID RPO Codes