Chevrolet 2003 Impala Owner's Manual page 147

Defogging and Defrosting
There are two modes to clear fog or frost from your
windshield. Use the defog mode to clear the windows of
fog or moisture and warm the passengers. Use the
defrost mode to remove fog or frost from the windshield
more quickly.
Turn the right knob clockwise to select the defog or
defrost mode.
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(Defog): This mode directs air equally to the
windshield and the floor outlets. When you select this
mode, the system turns off recirculation and runs
the air-conditioning compressor unless the outside
temperature is below 40°F (4°C). The recirculation mode
cannot be selected while in the defog mode.
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(Defrost): Pressing this button directs most of the
air to the windshield and the side window outlets,
with some air directed to the floor outlets. In this mode,
the system will automatically turn off recirculation
and run the air-conditioning compressor, unless the
outside temperature 40°F (4°C). Recirculation cannot be
selected while in the defrost mode.
Rear Window Defogger
The rear window defogger uses a warming grid to
remove fog from the rear window.
REAR: The rear defogger will turn off
approximately 15 minutes after the button is pressed.
An indicator light on the button will come on. If turned on
again, the defogger will only run for approximately
seven and one half minutes before turning off. The
defogger can also be turned off by pressing the button
again or by turning off the engine.
If your vehicle has heated outside rearview mirrors, the
mirrors will heat to help clear fog or frost from the
surface of the mirror when the rear window defog button
is pressed.
Notices Don't use anything sharp on the inside of
the rear window. If you do, you could cut or damage
the warming grid, and the repairs wouldn't be
covered by your warranty. Do not attach a temporary
vehicle license, tape, a decal or anything similar
to the defogger grid.
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