GMC 2003 Envoy XL Owner's Manual page 151

You may notice a slight change in engine performance
when the air-conditioning compressor shuts off and turns
on again. This is normal.
%
(Air Conditioning Off): When you turn the air
conditioning off, this symbol will appear on the display.
When the air conditioning is selected or in AUTO mode,
the system will run the air conditioning automatically.
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.
+3
(Defog): Use this setting to clear the windows of fog
or moisture. This setting will deliver air to the floor
and windshield outlets.
@
(Front Defrost): Press the front defrost button to
defrost the windshield. 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
The rear window defogger uses a warming grid to
remove fog from the rear window.
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.
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