1997 GMC Sonoma Owner's Manual - Page 118

Air Conditioning (Option) On hot days, open the windows long enough to let hot inside air escape. This reduces the time it takes for your vehicle to cool down. Then keep your windows closed for the airconditioner to work its best. For quick cool-down on very hot days, use MAX A/C with the temperature knob turned counterclockwise. 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 counterclockwise. On cool but sunny days, useBI-LEVEL A/C to deliver warm air tothe floor and cooler air to instrument the panel outlets. If you have the "VQRTEC 4300" engine, 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 clockwise. BLEND is useful in cool weather when you have fog or ice on the windshield or side windows. If you use the optional engine coolantheater before starting your engine, your heating system will produce warmer air fdster 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 VENT to direct outside air through your vehicle. Airflow is through the instrument panel outlets. Your vehicle's ventilation system supplies outside air to 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. 3-4