Chevrolet Silverado 2007 Owner's Manual page 250

Defogging and Defrosting
Fog on the inside of the 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. There
are two modes to clear fog or frost from
the windshield.
H G
Use and to select the defog or
defrost modes.
-
(Defog): Press this button to clear the
windows of fog or moisture and warm the
passengers. This mode directs air to the
windshield, floor outlets, and side window vents.
When this mode is selected, the system turns
off recirculation and runs the air conditioning
compressor unless the outside temperature is
close to freezing. The recirculation mode cannot
be selected while in the defog mode. Do not drive
the vehicle until all the windows are clear.
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(Defrost): Press this button to remove fog or
frost from the windshield more quickly. This
mode directs a portion of the air to the windshield
and side window vents and some to the floor
vents. In this mode, the system will automatically
force outside air into your vehicle. The
recirculation mode cannot be selected while in the
defrost mode. The air conditioning compressor
will run automatically in this setting, unless
the outside temperature is close to freezing. 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.
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(Rear Window Defogger): If your vehicle
has this feature, press this button to turn the
defogger on or off. It automatically turns off several
minutes after it has been activated. The defogger
can also be turned off by turning the engine
off. Do not drive the vehicle until all the windows
are clear.