A/C Mode

WARNING: This page is about a different car, the 2002 Pontiac Montana, 2002 Oldsmobile Silhouette, and 2002 Chevrolet Venture. However, it is still accessible from the selected car via links, so may be relevant.

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 allowed 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. 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 125 C (257 F).