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 placing the mode switch in any position and 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 module is in Vent, Bi-Level, or Off position. A/C operation is allows when outside air temperature is above 4°C (40°F).

The Powertrain Control Module (PCM) will operate the A/C system without any driver input. The PCM will command the A/C compressor clutch on to help reduce moisture inside the vehicle. The A/C compressor is on, even in cool weather conditions, to help eliminate moisture from fogging the windshield. The A/C LED will not illuminate unless the driver presses the A/C request switch on the HVAC control module. Otherwise, the A/C system may be running without the A/C LED indicator illuminated.

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 by the HVAC control module to the PCM through the A/C request signal circuit when the A/C switch grounds the 12 volt signal from the PCM. 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 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, located in the underhood junction block, provides a path for the voltage spike resulting from the collapsing magnetic field of the compressor clutch coil. 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. The PCM will shut off the A/C compressor under extreme vehicle loads, such as wide open throttle.

The PCM will shut off the A/C compressor under extreme vehicle loads. If system voltage falls below 10 volts, an A/C command will not be given until voltage is raised to 10.8 volts. If coolant temperature rises above 126°C (259°F) or the throttle is opened 95% or more, the compressor clutch will be turned off. Compressor operation will be allowed when the throttle is backed off to 90%.