Chevrolet 2002 Astro Owner's Manual page 156

Rear Window Defogger (Option)
If your vehicle has this option, the rear window will
have lines running across the glass. These lines heat
your window.
For best results, clear the window of as much snow or
ice as possible before using the rear window defogger.
Press the button until the light comes on, then release it.
To turn on the rear window
defogger, find the button
located to the left of the
heater controls with the
defog symbol on it.
The rear window defogger will only work when the
ignition is in RUN.
You can turn the defogger off at any time by pressing
the button again. The defogger will shut itself off after
several minutes so that the glass does not get too hot.
If the window still isn't clear, turn the defogger on again.
Do not attach a temporary vehicle license, tape or decals
across the defogger grid on the rear window.
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.
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