GMC 2008 Envoy - Manual (Page 161)

Defogging and Defrosting
Fog on the inside of the windows is a result of moisture
condensing on the cool window glass. This can be
reduced if the climate control system is used properly.
You can use either defog or front defrost to clear
fog or frost from your windshield.
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(Defog): Use this setting to clear the windows of
fog or moisture. This setting will deliver air to the
floor and windshield outlets.
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(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.
Rear Window Defogger
If your vehicle has the rear window defogger a warming
grid is used to remove fog from the rear window.
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(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.
If your vehicle has heated mirrors, they will come on
when this button is pressed.
Notice: Do not use a razor blade or sharp object to
clear the inside rear window. Do not adhere anything
to the defogger grid lines in the rear glass. These
actions may damage the rear defogger. Repairs
would not be covered by your warranty.
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