1999 Chevrolet Silverado 1500 Pickup Owner's Manual - Page 166

yellowblue Heating The heater works best if you keep your windows closed while using it. On cold days, use the HEATER or VENT/HEAT setting with the temperature knob in the red area. On cold days, approximately 32_F (-0_C) or lower, if your vehicle is equipped with a gasoline engine and automatic transmission, you may experience differences in how the transmission shifts until the engine is warm. This feature automatically reduces the time it takes for the engine to reach normal operating temperature and shortens the time it takes the heater to reach full output. If you use the engine coolant heater before starting your engine in cold weather, 20_F (-8_C) or lower, your heating system will produce warmer air faster, to heat the passenger compartment in cold weather. The use of an engine coolant heater also reduces the time it takes for the engine to reach normal operating temperature, and shortens the time it takes the heater to reach full output. For more information, see "Engine Coolant Heater" in the Index. Defogging and Defrosting On cool, humid days, use DEFOG to keep the windshield and side windows clear. Use DEFROST to remove fog or ice from the windshield in extremely humid or cold conditions. Use DEFROST with the temperature knob toward the red area and the fan control turned all the way to the right. Rear Window Defogger (If Equipped) If you see lines running across the rear window, you have a rear window defogger. The lines warm the glass. To turn on the rear window defogger, press this button next to the fan control knob. The rear window defogger will only work if the ignition switch is turned to RUN. For best results, clear the window of as much snow or ice as possible first. The defogger will shut itself off after several minutes. If you need additional warming time, press the button again. You can turn the defogger off at any time by pressing the button. 3-6