1993 GMC Suburban Owner's Manual - Page 149

K2315 You will find sir vents in the center and on the sides of your instrument panel, You canmovethevents to directtheflow ofair,or closethevents altogether.When you close, a vent, it will increase the flow of aircomingout of any vents that are open. If your vehicle does not have air conditioning, there are air vents below the instrumentpanel.Eachvent has ahandlewith a ventsymbolonit.Usethe handle to open and close thevent. 3-3