GM Service Manual Online
For 1990-2009 cars only

With this system you can control the heating, cooling, defrost, defog and ventilation for your vehicle.


Object Number: 879823  Size: B2

Manual Operation

Turn the right knob clockwise or counterclockwise to direct the airflow inside of your vehicle.

To change the current mode, select one of the following:

(Vent):  This mode directs air to the instrument panel outlets.

(Bi-Level):  This mode allows for approximately a 50/50 split of air to the instrument panel outlets and to the floor outlets.

(Floor): This mode directs most of the air to the floor outlets, with some of the air directed to the windshield and side window outlets. In this mode, the system will automatically select Outside Air.

The right knob can also be used to select defog or defrost mode. For more information, see "Defogging and Defrosting" later in this section.

It should be noted, that the air conditioning compressor will be engaged unless the outside temperature is 40° F (4°C) or below. Recirculation cannot be selected when in Floor Mode.

(Fan):  Turn the left knob clockwise or counterclockwise to increase or decrease the fan speed. If the airflow seems low when the fan is at the highest setting, the passenger compartment air filter, if equipped, may need to be replaced. For more information, see Passenger Compartment Air Filter and Part A: Scheduled Maintenance Services .

(Outside Air):  Press this button to turn the outside air mode on. When this mode is on, outside air will circulate throughout your vehicle. When the button is pressed, an indicator light in the button will come on to let you know that it is activated. The outside air mode can be used with all modes, but it cannot be used with the recirculation mode. You may have to set the instrument panel brightness control to the highest setting during the day to see the indicator lamp. The outside air mode can be used with all modes, but it cannot be used with the recirculation mode.

If you are in city traffic, your vehicle is stopped and idling, or the weather is hot, the system may switch from the outside air mode to the recirculation mode. To prevent the air inside of your vehicle from becoming too stale, be sure to return to the outside air mode periodically.

(Recirculation): This mode keeps outside air from coming in the vehicle. It can be used to prevent outside air and odors from entering your vehicle or help heat or cool the air inside your vehicle more quickly. Press this button to turn the recirculation mode on. When the button is pressed, an indicator light will come on. The air-conditioning compressor also comes on. You may have to set the instrument panel brightness control to the highest setting during the day to see the indicator lamp. The recirculation mode cannot be used with outside air modes.

D or P (Temperature Control):  Slide the levers marked D (Driver) or P (Passenger) to increase or decrease the temperature on the driver's side or the passenger's side of the vehicle.

A/C (Air Conditioning):  Press this button to turn the air-conditioning system on or off. When A/C is pressed, an indicator light will come on to let you know that air conditioning is activated. You may have to set the instrument panel brightness control to the highest setting during the day to see the indicator lamp.

On hot days, open the windows to let hot inside air escape; then close them. This helps to reduce the time it takes for your vehicle to cool down. It also helps the system to operate more efficiently.

For quick cool down on hot days, do the following:

  1. Select the vent mode.
  2. Select the recirculation mode.
  3. Select A/C.
  4. Select the coolest temperature for both zones.
  5. Select the highest fan speeds.

Using these settings together for long periods of time may cause the air inside of your vehicle to become too dry. To prevent this from happening, after the air inside of your vehicle has cooled, turn the recirculation mode off.

The air-conditioning system removes moisture from the air, so you may sometimes notice a small amount of water dripping underneath your vehicle while idling or after turning off the engine. This is normal.

Defogging and Defrosting

Fog on the inside of the windows is a result of high humidity (moisture) condensing on the cool window glass. This can be minimized if the climate control system is used properly. There are two modes to clear fog or frost from your windshield. Use the defog mode to clear the windows of fog or moisture and warm the passengers. Use the defrost mode to remove fog or frost from the windshield more quickly.

Turn the right knob clockwise to select the defog or defrost mode.

(Defog):  This mode directs air equally to the windshield and the floor outlets. When you select this mode, the system turns off recirculation and runs the air-conditioning compressor unless the outside temperature is below 40°F (4°C). The recirculation mode cannot be selected while in the defog mode. Do not drive the vehicle until all the windows are clear.

(Defrost): This mode directs half of the air to the windshield and side window vents and half to the floor vents. In this mode, the system will automatically force outside air into your vehicle. The recirculation mode cannot be selected while in the defog mode. The air conditioning compressor will run automatically in this setting, unless the outside temperature is below 40°F (4°C). Do not drive the vehicle until all the windows are clear.

Rear Window Defogger

The rear window defogger uses a warming grid to remove fog from the rear window.

REAR: The rear window defogger will turn off approximately 20 minutes after the button is pressed. If turned on again, the defogger will run for the same amount of time. The defogger can also be turned off by pressing the button again or by turning off the engine. Do not drive the vehicle until all the windows are clear.

If your vehicle has heated outside rearview mirrors, the mirrors will heat to help clear fog or frost from the surface of the mirror when the rear window defog button is pressed.

Notice: Do not use anything sharp on the inside of the rear window. If you do, you could cut or damage the warming grid, and the repairs would not be covered by the vehicle warranty. Do not attach a temporary vehicle license, tape, a decal or anything similar to the defogger grid.