1999 GMC Yukon Owner's Manual - Page 160

yellowblue Ventilation System For mild outside temperatures when little heating or cooling is needed, use VENT to direct outside air through your vehicle. Air will flow through the instrument panel outlets. Your vehicle's ventilation system supplies outside air to the inside of your vehicle when it is moving. With the side windows closed, air will flow into the front air inlet grilles, through the vehicle, and out the air exhaust valves. Outside air will also enter the vehicle when the heater or the air conditioning fan is running, unless you have the recirculation button pushed in. For more information on the recirculation button, see "Air Conditioning" earlier in this section. Your vehicle has air outlets in the center and on the sides of your instrument panel. You can move the outlets from side-to-side or up and down to direct the flow of air, or close the outlets altogether. When you close an outlet, it will increase the flow of air coming out of any outlets that are open. These outlets do not completely shut off airflow when in a closed vent position. 3-8