2001 GMC Sierra 1500 Pickup Owner's Manual - Page 201

The defogger will shut itself off after several minutes. If you need additional warming time, press the button again. You can turn the defogger off at any time by pressing the button. If your vehicle is equipped with heated outside mirrors, the rear window defogger button will also activate the heated outside mirrors. Do not attach a temporary vehicle license, tape or decals across the defogger grid on the rear window. Ventilation System For mild outside temperatures when little heating or cooling is needed, use VENT to direct outside air through your vehicle. Air will flow through the instrument panel outlets. Your vehicle's ventilation system supplies outside air to the inside of your vehicle when it is moving. With the side windows closed, air will flow into the front air inlet grilles, through the vehicle, and out the air exhaust valves. Outside air will also enter the vehicle when the heater or the air conditioning fan is running, unless you have the RECIRCULATION button pushed in. For more information on the RECIRCULATION button, see "Air Conditioning" earlier in this section. NOTICE: Don't use a razor blade or something else sharp on the inside of the rear window. If you do, you could cut or damage the warming grid, and the repairs wouldn't be covered by your warranty. 3-14