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 HVAC switch is pressed. 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 A/C LED will flash, indicating that A/C is not allowed. The A/C compressor is activated when FROST DEFROST is selected. A/C will not be allowed if engine RPM exceeds 5985.

The HVAC control module receives power from the instrument panel fuse block on the ignition 3 voltage circuit along with the battery positive voltage circuit. The module is grounded by the ground circuits and splice pack. The HVAC control module communicates directly to the PCM on the class 2 serial data and the ECM/PCM/VCM class 2 serial data circuits through the splice pack.

The PCM will engage the A/C 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.
^ The A/C compressor cycling switch pressure is less than 124 kPa (18 psi) or more than 338 kPa (49 psi).
^ The A/C high pressure cutout switch pressure is more than 2896 kPa (420 psi).
^ Engine speed is more than 5500 RPM.
^ Engine coolant temperature (ECT) is more than 121°C (250°F).

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 through the A/C request signal circuit, through the A/C high pressure switch, from the HVAC control module.

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 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. The ground circuit and underhood fuse block provides a path to ground for the compressor. The A/C clutch relay control circuit is grounded internally within the PCM.