Have 2001 2500 HO Diesel. A/C, heat, and vent all work as per temp and volume, but only comes out the defrost vents. Also seems to blow warm air out floor vent when in A/C Max mode at the same time cold air comes out defrost.

On a side note ~~ is it possible that an intake vent inside the cab has sucked up trash? If so, how do I get to it to clean it out?

 

The door is not moving, check the hoses going to the control unit.

 

its either a vacuum hose, line to it or the check valve.

 

Had exactly this problem about a month ago. After checking that the vacuum to controller was fine, I looked under the dash and discovered the pin on the panel/defrost door had broken and the only way to get to it...was to take the dash off [&:]Believe me I tried everything else, and after getting it dismantled we had to take the p/d door out to drill out the old pin that had broken off to replace it. Once we got everything back together it worked like a charm...except for a slight dash rattle. It only took about 4 hours from start to finish thanks to the service manual I was able to download from this forum...a real lifesaver!
Good luck,
Marilyn