A/C Mode: Notes

WARNING: This page is about a different car, the 2002 Oldsmobile Intrigue. 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 A/C system can operate regardless of the temperature setting, as long as the ambient temperature is above 38°F (3.3°C). The automatic HVAC system will provide A/C in the most efficient manner. On initial engine start-up, the blower motor will come on at low blower speeds to purge the HVAC module of moisture momentarily. To cool the interior of the vehicle quickly, maximum cool mode is used where the blower is at maximum speed, vent mode, air temperature is in full cold and the recirculation is drawing air from inside of the vehicle. Setting the temperature to 60°F (16°C) will lock the HVAC control module in full cold and recirculation mode. The AUTO LED will not illuminate. The HVAC control module will not control the system automatically until the set temperature is raised from 60°F (16°C). Once the temperature setting is raised, the AUTO switch will have to be pressed again to activate the automatic HVAC system. The AUTO LED will then illuminate.

In all A/C mode settings, the HVAC class 2 serial data circuit request the Powertrain Control Module (PCM) to turn ON the A/C compressor. The PCM turns ON the A/C compressor by providing a path to ground through the A/C compressor clutch relay control circuit of the A/C compressor clutch relay. Battery positive voltage is provided to the A/C compressor clutch relay from the underhood fuse block and ignition main relay. When the A/C compressor clutch relay closes its internal switch, battery positive voltage is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit. When the compressor disengages, the A/C compressor clutch diode absorbs the voltage surge. This surge results from the collapsing magnetic field of the compressor clutch coil. The ground circuit provides a path to ground for the A/C compressor clutch. The control circuit of the A/C compressor clutch. The control circuit of the A/C compressor clutch relay is grounded internally within the PCM.

The PCM will engage the compressor 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 (WOT).
Vehicle Launch (Acceleration from a stop).
Idle Quality.
A/C refrigerant pressure sensor is more than 432 psi (2979 kPa) or less than 27 psi (186 kPa).
Engine speed is more than 5500 RPM.
Engine Coolant Temperature (ECT) is more than 255°F (124°C).
Transmission Shift Engine Torque Load.