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 assembly is in any mode other than FRONT DEFROST and MIX-BLEND.

The Powertrain Control Module (PCM) will operate the A/C system automatically in FRONT DEFROST or MIX-BLEND modes to help reduce moisture inside the vehicle. The A/C LED will not illuminate unless the driver presses the A/C request switch on the HVAC control assembly. The A/C system may be running without the A/C LED indicator illuminated when in FRONT DEFROST or MIX-BLEND modes. 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 body control module (BCM) to turn on the A/C compressor. The request is made by the HVAC control assembly to the BCM, through the A/C request signal circuit. When the BCM receives the signal from the HVAC control module, the BCM then sends a class 2 message to the PCM through the class 2 serial data circuit. The PCM grounds the A/C clutch relay control circuit and the A/C compressor clutch engages. Power is provided to the HVAC control assembly by the left IP fuse block and the underhood fuse 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 underhood fuse block. Once the relay closes its internal switch, battery voltage 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 path to ground for the compressor and relay. The A/C clutch relay control circuit is grounded internally within the PCM.