2008 Chevrolet Silverado 1500 Pickup Owner's Manual - Page 205

Defogging and Defrosting Fog or frost on the inside of 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. To avoid fogging windows on rainy and humid days at temperatures above freezing, run the air conditioning compressor. It is best to avoid the use of the recirculation mode, except when maximum A/C performance is needed or for short times to avoid exterior odors. Turn the right knob to select the defog or defrost mode. Rear Window Defogger If your vehicle has a rear window defogger it uses a warming grid to remove fog from the rear window. The rear window defogger will only work when the ignition is in RUN. < (Rear): Press this button to turn the rear window defogger on or off. An indicator light on the button will come on to let you know that the rear window defogger is activated. The rear window defogger will only work when the ignition is in RUN. The rear window defogger will stay on for approximately 10 minutes after the button is pressed, unless the ignition is turned to ACC or LOCK. The defogger can also be turned off by pressing the button again or by turning off the engine. 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. - (Defog): This mode clears the windows of fog or moisture and warm the passengers. The air is directed to the windshield, floor outlets, and side window vents. 0 (Defrost): This mode removes fog or frost from the windshield more quickly. A portion of the air is directed to the windshield and the side window vents, with some air directed to the floor vents. The system will automatically force outside air into the vehicle. The recirculation mode cannot be selected in the defog or defrost mode. When either mode is selected, the system runs the air conditioning compressor, unless the outside temperature is close to freezing. Do not drive the vehicle until all the windows are clear. 3-27