Heating And A/C Operation: Notes

WARNING: This page is about a different car, the 2002 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 assembly. 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 40°F (4°C)
Engine Coolant Temperature (ECT) Is Less Than 255°F (124°C) For The LG8 And 250°F (121°C) For The L36
Engine RPM Is Less Than 5000 RPM.
A/C Pressure Is Between 27-432 Psi (186-2979 kPa)

Once engaged, the compressor clutch will be disengaged for the following conditions:

Throttle Position Is 100 Percent
A/C Pressure Is More Than 432 Psi (2979 kPa)
A/C Pressure Is Less Than 27 Psi (186 kPa)
Engine Coolant Temperature (ECT) Is More Than 255°F (124°C) For The LG8 And 250°F (121°C) 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.