2004 GMC Envoy Owner's Manual - Page 149

Defogging and Defrosting Fog 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. You can use either defog or front defrost to clear fog or frost from your windshield. Use this setting to clear the windows of fog or moisture. This setting will deliver air to the floor and windshield outlets. Rear Window Defogger The rear window defogger uses a warming grid to remove fog from the rear window. < (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 activated. The rear window defogger will turn off approximately 10 minutes after the button is pressed. If you need additional warming time, press the button again. Notice: Using a razor blade or sharp object to clear the inside rear window may damage the rear window defogger. Repairs would not be covered by your warranty. Do not clear the inside of the rear window with sharp objects. -(Defog): 0 (Front Defrost): Press the front defrost button to clear the windshield and side windows of frost or fog quickly. The system will automatically control the fan speed if you select defrost from AUTO mode. If the outside temperature is 40°F (4°C) or warmer, your air conditioning compressor will automatically run to help dehumidify the air and dry the windshield. Do not drive the vehicle until all the windows are clear. 3-29