2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 246

? (Recirculation): Press to turn the recirculation mode on. An indicator light comes on to show that recirculation is on. This mode recirculates and helps to quickly cool the air inside the vehicle. It can be used to help prevent outside air and odors from entering the vehicle. The recirculation mode cannot be used with floor, defog or defrost modes. If recirculation is selected with one of these modes, the indicator light flashes three times and then turns off. While in recirculation mode the windows may fog when the weather is cold and damp. To clear the fog, select either the defog or defrost mode and increase the fan speed. The recirculation mode can be turned off by pressing the outside air button, or by turning off the ignition. # (Air Conditioning): Press to turn the air conditioning system on or off. An indicator light comes on to show that the air conditioning is on. The air conditioning can be selected in any mode as long as the fan switch is on. The air conditioning system removes moisture from the air, so a small amount of water might drip under the vehicle while idling or after turning off the engine. This is normal. Rear Window Defogger For vehicles with a rear window defogger, a warming grid is used to remove fog from the rear window. < (Rear): Press to turn the rear window defogger on or off. An indicator light on the button comes on to show that the rear window defogger is on. The rear window defogger only works when the ignition is in ON/RUN. The rear window defogger stays on for approximately 10 minutes after the button is pressed, unless the ignition is turned to ACC/ACCESSORY or LOCK/OFF. The defogger can also be turned off by turning off the engine. Notice: Do not use anything sharp on the inside of the rear window. If you do, you could cut or damage the warming grid, and the repairs would not be covered by the vehicle warranty. Do not attach a temporary vehicle license, tape, a decal or anything similar to the defogger grid. 4-22