I recently bought my dad's 02 2500 Cummins. Great truck but AC/heater temp knob does not work. Don't matter what position it's in, mainly blows hot air like the heater is wide open. Occasionally it is stuck in AC mod,blowing cold air. My dad replaced the heater core before I got the truck,taking out the dash in the process. I figure this is what started the problem. Is the temp control knob manually controlling a valve by some sort of cable, or is it an electical switch? I'm just trying to get ideas before I start digging into the dash. Thanks for the help.