1997 GMC Suburban Owner's Manual - Page 158

Ventilation System For mild outside temperatures when little heating or cooling is needBd, use VENT to -directoutside air through your vehicle. Air will flow though the instrument panel outlets. Your vehicle's ventilation system supplies outsideair to the inside your vehicle when it is moving. Wt of ih the side windows closed, air will flow into the h a t air inlet grilles, though the vehicle, and out the air exhaust valves. Outside air will also enter the vehicle when the heater qr the air conditioning fan is running, unless you have the recirculation button pushed in. For more infomation on the recirculation button, see "Air C~onditiQning" earlier in this section.