1998 Chevrolet Astro Owner's Manual - Page 160

Rear Window Defogger (Option) If your vehicle has this option, rear window will the have lines running across the glass. These lines heat your window. For best results, clear the window ofas much snow or ice as possible before using therear window defogger. The rear window defogger will only work when the ignition switch i s in the RUN position. You can turn the defoggeroff at any time by pressing the button again. The defogger will shut itselfoff after several minutes so that the glass does not get too hot. If the window still isn't clear, turn the defogger on again. To turn on the rear window defogger, find the buttonto the left of the heater controls with the defog symbol on it. Do not attach a temporary vehicle license, tapeor decals across the defoggergrid on the rear window. 1 NOTICE: 1 Don't use a razor blade something else sharp or on the insideof the rear window. If you do, you could cut or damage the defogger and the repairs would not be covered by your warranty. Press the button until the light comes on, then release it. 3-8