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 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. The request is made to the PCM through the A/C request signal circuit from the HVAC control module. Power and ground are provided to the HVAC control module by the ignition 3 voltage, binary positive voltage, ground circuits and splice pack.

In order for the PCM to internally ground the A/C clutch relay control circuit, the request signal needs to be grounded. A 12-volt request signal is sent out over the A/C request signal circuit and grounded through the HVAC control module when the vehicle operator makes an A/C request. When this request signal is grounded, the PCM can activate the A/C compressor clutch.

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 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 PCM monitors the A/C compressor clutch status on a separate A/C compressor clutch supply voltage circuit. The ground circuit and splice pack provides a path to ground for the compressor. The A/C clutch relay control circuit is grounded internally within the PCM.