1993 GMC Suburban Owner's Manual - Page 150

... L, Y - K2441 If your. vehicle does not have air conditioning, this system will look like. is what your heating F ~ Knob R Theknobontherighthasfourpositions. toward (t). To decreasetheairflow,turn To increasetheairflow,turn it toward (-). it Temperature kewer The bottom lever lets you select the temperature of the air flowing into your vehicle.Movetheleverrighttoward (t) forwarmerair.Movetheleverleft toward (-) forcoolerair. Fune%ionLewer Thetoplevercanbemoved to three different heating functions, Defrost (Right): Thissettingoperatesthedefroster.Heatedaircomesout the windshield. nearthewindshield.Usethiswhenyougetfogoriceon Heater(Center): Heated air comes out near the floor. This weather. Vent(Left): Theaircomesout at your front side windows. is best for cold at the vents on your instrument panel and Placing the lever between positions sends air out both vents.