I have an 03, 2500 Ram, Cummins Diesel, 4WD automatic.
The HVAC control for the temp seems to only switch from extreme hot to extreme cold. I have removed the glove box and most of my dash and watched as the servo/actuator thing moved steadily from one extreme to the other as I slowly adjusted the temp control dial. I even moved the dial one 'click' at a time and watched the servo/actuator thing stop at each graduation as I stopped moving the control dial. Unfortunately, none of this seems to do anything to actually modify the air temp coming from the vents. Sometimes it is just cold, sometimes just hot, and sometimes just barely warm, but regardless of what comes out of the vents, it stays at that temp for the duration of my drive. It is different for just about each trip I take, sometimes it is hot, sometimes cols... you get the idea. Anyways, I have visually verified that the motorized servo/actuator thing does work in conjunction with turning the temp control dial (works with the fan on as well as off). Is there something inside the box that is likely to be broken? Can anyone point me to an online resource or exploded view of the HVAC box that could give me an inside view before I try to take the whole thing apart myself? Is this a common issue with the 3rd Generation Ram trucks?
Thanks to all in advance.

 

Exploded view

 

Thanks (Parts/Service), The image was a bit too small to use, even when enlarged. But I did go out and find the free version of the 03DRM.pdf online. Is this the correct version for my 03 Ram 2500 Diesel 4x4? Does my problem sound like a blend door issue to you? If so, is it possible to replace the blend door without a complete dissasembly of my dash and HVAC box?
Man, I really wish Chrysler would have engineered this truck as well as Cummins did for the engine. I have a feeling that I will be using the engine as a generator powerplant long after I am unable to continue using the truck.

 

everybody i know that has owned a dodge truck 2001 or newer has experienced this problem at one time or another. The door flap itself sometimes breaks, its plastic and the little plastic nubs break off the 'hinge' on the piece and it LOOKS like it still moves, however when braking and accelerating it causes it to swing to one extreme or the other. I had nice cold air in my 2001 until i touched the brakes, it would go directly to heat. On a 2006 Diesel, it simply stuck on hot and never moved. On a friend of mine's 02, he had random hot and cold and I couldn't find an event to trigger it. Several others in the 2001+ range I know have had the same/similar problems.