I have a 99 dodge 2500 diesel that the AC will only blow cold all the way on cold and the heater will only get hot all the way on heat there is no in between could that be the switch or a blend door?

 

Look under your dash, at the heater box, right above the trans tunnel, towards the passenger side. There *might* be a little motor there, that controls the blend door. (not sure what the first year for that was......) If there is, chances are good the coupler between the motor, and the axle for the blend door has split. HeaterTreater.net has the fix for that.

 

Thanks for the information I will check that if I have to remove the heater box I will replace the AC evaporate rand heater core while there.

 

The little bushing for the blend door fixed that problem I went ahead and changed the evap. Core and heater core while I was there also replaced expansion vale which was the whole line it took me about 5 hours to do the job thanks for the help 99RedRam99

 

Awesome. Nice cold air, and hot heat now? (and anything in between? )