2004 GMC Envoy Owner's Manual - Page 144

Rear Window Defogger Your vehicle may have this feature. The lines you see on the rear window warm the glass. Outlet Adjustment Use the air outlets located in the center and on the side of your instrument panel to direct the airflow. < (Rear): Press this button to turn the rear window defogger on or off. An indicator light in the button will come on to let you know that the rear window defogger is active. The rear window defogger will automatically turn off approximately ten minutes after the button is pressed. If your vehicle is equipped with heated mirrors, this button will activate them. Notice: Don't use anything 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. Do not attach a temporary vehicle license, tape, a decal or anything similar to the defogger grid. Ventilation System For mild outside temperatures when little heating or cooling is needed, use the vent setting to direct outside air through your vehicle. 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 is running, unless you have selected recirculation mode. 3-24