Heating And A/C Operation

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 heating and A/C system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. The vehicle operator can determine the passenger compartment temperature by adjusting the air temperature switch. Regardless of the temperature setting, the following can effect the rate that the HVAC system can achieve the desired temperature:

Recirculation
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. The A/C switch will illuminate when the A/C switch is pressed to the on position. The following conditions must be met in order for the PCM to turn on the compressor clutch:

Engine Coolant Temperature (ECT) Is Less Than 255°F (124°C)
Engine Speed Is Less Than 5000 RPM
A/C Pressure Is 432-27 Psi (2979-186 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)
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.