Heating and A/C Operation

WARNING: This page is about a different car, the 2003 Pontiac Montana, 2003 Oldsmobile Silhouette, and 2003 Chevrolet Venture. However, it is still accessible from the selected car via links, so may be relevant.

Obtaining proper HVAC maximum cooling operation:

Open the windows to allow the escape of hot interior hot air
Press the A/C button the A/C LED will illuminate on the A/C button
Set the mode switch to outside air
Set the fan control to the 5 or high setting
Set the temperature knob to the full cold setting by turning it counterclockwise
After 90 seconds, push the Recirculation button the Recirc LED on the Recirc button will illuminate
Close the windows

This procedure acts as a purge of the hot passenger compartment air while allowing cool air conditioned air to fill the passenger compartment. The outside air button should be pushed once a desired comfort level has been achieved.

The control module makes the following actions when making a climate selection, and an air temperature setting is selected:

When the air temperature switch is placed in the warmest position, the control module commands the air temperature door to divert maximum air past the heater core.
When the air temperature switch is placed in the coldest position, the control module commands the air temperature door to direct air to bypass the heater core.

Pressing the A/C switch engages the A/C system and illuminates the A/C switch LED. The HVAC control module sends a 5-volt request signal to the powertrain control module (PCM). The HVAC system uses a scroll compressor that incorporates a thermal switch that opens once the compressor temperature is more than 155°C (311°F). The thermal switch is a non-serviceable item. The following conditions must be met in order for the PCM to turn on the compressor clutch:

HVAC control module
Evaporator Temperature more than 2°C (36°F)
PCM
- Engine coolant temperature (ECT) is more than 125°C (257°F)
- Engine RPM is less than 5,000 RPM
- A/C Pressure is between 1620-2979 kPa (235-432 psi)
- Ambient temperature more than 4°C (40°F)
- A/C request from the HVAC control module
- Battery voltage between 10.8-16 volts

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

Compressor thermal switch is opened
Throttle position is 100 percent
Battery voltage below 10 volts
A/C Pressure is more than 2979 kPa (432 psi)
A/C Pressure is less than 1620 kPa (235 psi)
Engine coolant temperature (ECT) is more than 125°C (257°F).
Engine speed is more than 5,500 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.