Heating and A/C Operation

WARNING: This page is about a different car, the 2003 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.

The purpose of the heating and A/C system is to provide the following:

Heated air
Cooled air
Remove humidity from the interior of the vehicle
Reduce windshield fogging
Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve the desired temperature:
Recirculation actuator setting
Difference between inside and desired temperature
Difference between ambient and desired temperature
Blower motor speed setting
Mode setting
The A/C system can be engaged by pressing the A/C switch or by selecting the following modes:
Bi-level
Front Defrost
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. The following conditions must be met in order for the PCM to turn on the compressor clutch:
Ambient air temperature is above 4°C (40°F).
Engine coolant temperature (ECT) is less than 124°C (255°F) for the LG8 and 121°C (250°F) for the L36.
Engine RPM is less than 5000 RPM.
A/C Pressure is between 186-2979 kPa (27-432 psi).
Once engaged, the compressor clutch will be disengaged for the following conditions:
Throttle position is 100%.
A/C Pressure is more than 2979 kPa (432 psi).
A/C Pressure is less than 186 kPa (27 psi).
Engine coolant temperature (ECT) is more than 124°C (255°F) for the LG8 and 121°C (250°F) for the L36.
Engine speed is more than 5000 RPM.
Transmission shift
PCM detects excessive torque load
PCM detects insufficient idle quality
PCM detects a hard launch condition
When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.