1998 GMC Envoy Owner's Manual - Page 138

Air Conditioning On hot days, open the windows long enough tolet hot inside air escape. This reduces the time it takes for your vehicle to cool down. Then keep yourwindows closed for the air conditioner to work its best. For quick cool-down on very hot days, A/C should be enabled with the temperature knob turned to the left and the OUTSIDE AIR button should not be active. This setting should be used to keep odors and/or dust from entering the vehicle. For normal cooling on hot days, use A/C with the temperature knob turned to the left. On cool but sunny days, use BI-LEVEL A/C to deliver warm air to the floor and cooler air to the instrument panel outlets. When the air conditioner is on, you may sometimes notice slight changes in your vehicle's engine speed and power. This is normal because the system is designed to cycle the compressor on and off to keep the desired temperature. Heating The heater works best if you keep your windows closed while using it. On cold days, use HEATER with the temperature knob turned to the right. BLEND is useful in cool weather when you have fog or ice on the windshield or side windows. If you use the optional engine coolant heater before starting your engine, your heating system will produce warmer air faster to heat the passenger compartment in cold weather. See "Engine Coolant Heater" in the Index. Ventilation System For mild outside temperatures when little heating or cooling is needed, use PANEL with the OUTSIDE AIR button enabled to direct outside air through your vehicle. Airflow is through the instrument panel outlets. Your vehicle's ventilation system supplies outside airto the inside of your vehicle when it is moving. When the vehicle is not moving, you can get outside air to flow through by selecting any mode and any fan speed. 3-5