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 placing the mode switch in one of the following positions: Max, Norm, Bi-Level, Blend, and Def. The A/C system can operate regardless of the air temperature setting. 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 powertrain control module (PCM) to turn on the A/C compressor clutch. The request is sent to the PCM through the A/C request signal circuit from the HVAC control assembly. Power and ground is provided to the HVAC control assembly by the ignition 3 voltage and ground circuits.

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. The ignition 1 voltage circuit provides power to the A/C compressor clutch relay control. Once the relay contact 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 entering the vehicles electrical system. The ground circuit provides a pathway to ground for the compressor. Both the A/C request signal and A/C clutch relay control circuits are grounded internally within the PCM.