All summer long I used the Auto function for Controling the climate in my Truck. It worked just fine. As it cooled down I turned off the auto function and opened up the windows and Sunroof. Of course I have seen an increase in my MPG. This week it has cooled down enough to need some heat in the truck. So I pushed the button for Auto climate control. So I am wondering after fiddling with the Climate control buttons... that even though I am heating the truck it seems as if the AC is running ( When I get out of auto mode the display says AC ON). Is my AC on even though I am heating my truck and will it impact my gas mileage.