Pontiac 2005 Bonneville Owner's Manual page 143

There is also an EXT (exterior) temperature sensor
located behind the front grill. This sensor reads
the outside air temperature and helps to maintain the
temperature inside the vehicle. Any cover on the front of
the vehicle could cause a false reading in the
temperature.
Defogging and Defrosting
Fog on the inside of windows is a result of high humidity,
or 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 your windshield. Use the defog mode to clear
the windows of fog or moisture and warm the
passengers. Use the FRONT defrost mode to remove
fog or frost from the windshield more quickly.
Press the MODE button until DEFOG appears to select
this function. Press the FRONT button to select the
defrost function.
DEFOG: This mode directs the air equally between the
windshield and the floor outlets.
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FRONT (Defrost): Pressing this button directs
most of the air to the windshield and the outboard outlets
for the side windows, with some air directed to the
floor outlets. When you select this mode, the system
turns off recirculation and runs the air conditioning
compressor unless the outside temperature is at
or below freezing. The recirculation mode cannot be
selected while in the FRONT defrost mode. 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 or frost from the rear window.
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REAR: Press this button to turn the rear window
defogger on or off. Be sure to clear as much snow from
the rear window as possible.
The rear window defogger will turn off about 10 minutes
after the button is pressed. If turned on again, the
defogger will only run for about five minutes before
turning off. If you maintain a speed above 30 mph
(48 km/h), the rear defogger will not turn off
automatically to help keep the rear glass clear. The
defogger can also be turned off by pressing the button
again or by turning off the engine.
If your vehicle has outside heated mirrors, the mirrors
will heat to help clear fog or frost from the surface of the
mirror when the rear window defogger button is
pressed.
Notice: Using a razor blade or sharp object to clear
the inside rear window may damage the rear
window defogger. Repairs would not be covered by
your warranty. Do not clear the inside of the rear
window with sharp objects.
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