A/C Mode

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 any mode other than Blend, Floor or Defrost.

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 on the class 2 serial data circuit. The request is made by the HVAC control module to the BCM through the A/C request signal circuit when the A/C switch grounds the 12-volt signal from the BCM. The BCM then sends a class 2 message to the PCM on the BCM class 2 serial data circuit. The PCM grounds the clutch relay control circuit and engages the A/C compressor clutch. Power is provided to the HVAC control module by the console junction block through the ignition 3 voltage, which is routed through the splice pack, and the battery positive voltage circuits. 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 internally through 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 oft, the A/C compressor clutch diode, located in the underhood junction block, 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.

The BCM or 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 10.5 volts. If coolant temperature rises above 126°C (259°F) or the throttle is opened 95 percent or more, the compressor clutch will be turned off.