1999 Pontiac Grand Prix Owner's Manual - Page 160

yellowblue Heating On cold days use LOWER. The system will bring in outside air, heat it and send it to the floor ducts. If your vehicle has an engine coolant heater, you can use it to help your system provide warm air faster when it's cold outside 0_F (-18_C) or lower. An engine coolant heater warms the coolant your engine and heating system uses to provide heat. See "Engine Coolant Heater" in the Index. Ventilation For mild, outside temperatures when little heating or cooling is needed, use UPPER with the A/C button off, to direct outside air through your vehicle. Your vehicle also has the flow-through ventilation system described later in this section. Defogging and Defrosting Your system has two settings for clearing the front and side windows. To defrost the windows quickly, use DEF. To warm passengers while keeping the windows clean, use DEFOG. Your comfort control system has a button to operate your rear window defogger. The electronic comfort control system has a button marked REAR. The system with automatic temperature control has a button marked R.DEF. Rear Window Defogger 3-8