Pontiac 2004 Grand Prix Owner's Manual page 132

Recirculation
h
(Recirculation): Press this button on the climate
control panel to activate the recirculation mode. With
this selection inside air is recirculated into the vehicle
along with some outside air. This mode reduces outside
air and odors from entering your vehicle. It may also
help to heat or cool the air inside your vehicle more
quickly.
When this button is pressed an indicator lamp to the
right of the button will come on to indicate that the
recirculation mode is on. An adjustment to the
instrument panel brightness control to the highest
setting may be required to see the indicator lamp.
The recirculation mode has a timer. After five minutes,
the system's air inlet door will move slightly to allow
for ten percent fresh outside air to maintain interior air
quality. The only way to reset the system to full
recirculation is to restart the five minute timer by
selecting vent/outside air and recirculation again.
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Rear Window Defogger
The rear window defogger uses a warming grid to
remove fog or frost from the rear window. Be sure to
clear as much snow from the rear window as possible.
Notice: Don't use a razor blade or something
else sharp on the inside of the rear window. If you
do, you could cut or damage the defogger 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.
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(REAR): Press this button to turn the rear window
defogger on or off.
When this button is pressed an indicator light to the right
of the button will come on to show that the rear window
defogger is active. The instrument brightness control may
have to be adjusted to the highest setting during the
daytime in order to see the indicator light.
The rear window defogger will turn off approximately
20 minutes after the button is pressed. If reselected,
it will run another 20 minutes. The defogger can
be turned off by pressing the button again or by turning
off the engine.
Do not drive the vehicle until all windows are clear.