I have a 2004 cummins, when I turn my a/c on it will blow just fine out of the vents, then all the sudden it quits blowing out of the vents and starts coming out of the defrost vents. I have tried turning the control **** but nothing happens, it just blows out of the defrost vents. It will do this until I shut the truck off for a while. Any ideas on what it might be and where I can get the parts to fix it. thanks

 

That door is a tough one to replace in the truck. try heatertreater.com for info. Could be the defrost mode door. They are numbered, just dont remember what number its called.

You might check the servo motor also.

The door is right behind the console area in the dash.

Maybe someone will post the thread with the pics. Cant remember what its named.

I guess I cant remember much.. I replaced all my doors with heatertreater doors when I had to replace my heater core a while back.

That has been one of the best mods to my truck yet. Well out of the mods I remember doing.

 

darn, how do I know if its the door or an actuator. I wonder if its in the control head where the **** is? I guess I am going to have tear it apart, maybe I should sell it and go back to a chevy.

 

https://www.dieseltruckresource.com/....html?t=170393

There's a lot of good info on the subject at this link.