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. A/C is available as long as ambient air temperatures are above 4°C (40°F). When the vehicle operator presses the A/C switch, voltage is sent to the PCM through the A/C request signal circuit. When the PCM reads voltage on this circuit, the module knows that an A/C request has been made. 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.

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 from the underhood fuse block. Once the relay closes its internal switch, power 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 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 2979 kPa (432 psi) or is less than 186 kPa (27 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