Chevrolet Silverado 2007 Owner's Manual page 242

Turn the right knob to select the defog or
defrost mode.
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(Defog): This mode clears the windows of fog
or moisture and warm the passengers. The air
is directed to the windshield, floor outlets, and side
window vents.
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(Defrost): This mode removes fog or frost
from the windshield more quickly. A portion of the
air is directed to the windshield and the side
window vents, with some air directed to the floor
vents. The system will automatically force
outside air into the vehicle.
The recirculation mode cannot be selected in the
defog or defrost mode. When either mode is
selected, the system runs the air conditioning
compressor, unless the outside temperature
is close to freezing. Do not drive the vehicle until
all the windows are clear.
242
Rear Window Defogger
If your vehicle has a rear window defogger it uses
a warming grid to remove fog from the rear
window.
The rear window defogger will only work when the
ignition is in RUN.
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(Rear): Press this button to turn the rear
window defogger on or off. An indicator light on
the button will come on to let you know that
the rear window defogger is activated.
The rear window defogger will only work when the
ignition is in RUN. The rear window defogger
will stay on for approximately 10 minutes after the
button is pressed, unless the ignition is turned
to ACC or LOCK. The defogger can also be turned
off by pressing the button again or by turning off
the engine.
Notice: Do not use anything sharp on the
inside of the rear window. If you do, you could
cut or damage the warming grid, and the
repairs would not be covered by your warranty.
Do not attach a temporary vehicle license,
tape, a decal or anything similar to the
defogger grid.