General Description

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 manually 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 temperature setting, as long as outside ambient temperature is above 4°C (40°F). If the A/C is requested and temperatures are too low, the LED will flash 3 times to remind the vehicle operator that A/C is not available.

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 sent 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 fuse block through the ignition 3 voltage and ground circuits.

In order for the PCM to internally ground the A/C clutch relay control circuit, two separate request signals need to be grounded. A 12-volt reference signal is sent out over the A/C request signal circuits, through the A/C high pressure switch and grounded through the HVAC control module when the vehicle operator makes an A/C request. A separate 12-volt reference signal is sent out over the A/C refrigerant low pressure cut-out switch signal circuit, through the A/C low pressure switch and the ground circuit. When both these reference signals are 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 engine wiring harness junction 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 provides a path for the voltage spike resulting from the collapsing magnetic field of the compressor clutch coil. The ground circuit provides a pathway to ground for the compressor. The A/C clutch relay control circuit is grounded internally within the PCM.