1999 GMC Safari Owner's Manual - Page 144

yellowblue Function Knob This knob is next to the temperature knob. The function knob allows you to choose the direction of air delivery. OFF: This setting turns the system off. VENT: The air comes out at the vents on your instrument panel. BI-LEVEL: With this setting, the heated outside air comes out both the instrument panel vents and heater vents. Adjust the temperature knob for warmer or cooler air. HEATER: Most of the air comes out near the floor. The rest comes out from the defroster vents under the windshield and at the front side windows. BLEND: With this setting, the heated outside air comes out both the heater vents and defroster vents. Adjust the temperature knob for warmer or cooler air. DEFROST: This setting operates the defroster. Most of the air comes out near the windshield, with some going to the floor vents and front side windows. You may have the optional rear heater. The three-speed fan switch is to the right of the radio. Turn the switch toward HIGH for higher airflow in the rear area. Turn the switch to the OFF position to turn the system off. Rear Heating System (Option) 3-4