2008 GMC Sierra 1500 Pickup Owner's Manual - Page 160

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. Climate Control System (Heater Only) With this system you can control the heating and ventilation for your vehicle. < (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 your warranty. Do not attach a temporary vehicle license, tape, a decal or anything similar to the defogger grid. Operation 9(Fan): Turn the left knob clockwise or counterclockwise to increase or decrease the fan speed. Turn the knob all the way counterclockwise to turn the front system off. 3-24