I'm not the sharpest knife in the drawer on mechanics, but I try. My 2002 Dodge Ram 3500 Van blows only out the defrost...like so many others posted on this site. I've pulled the vacuum check valve located behind the control panel. Check valve allows flow in one direction, not in other. Input line has nearly 200 lbs vacuum. So these seem ok, Now I just need you to remind me which direction to install it. I've read there's a second check valve near the throttle body. Is it same as the one behind the controls or altogether different? Possible source of problem? Regarding finding replacement parts for these check valves, best I can find is a universal available from NAPA. Advice, please.

 

If the vents aren't switching, it's gotta be a vacuum problem.... if you are getting vacuum TO the control head, check at the various actuators...... that vacuum is going somewhere. One leak, and you are done.

 

UPDATE: I found hanging not attached a major vacuum line that sucks like heck. It has a rubber nipple on it and was hanging in the engine compartment near the A.C unit on the passenger side. But darned if I can find where it plugs in. The other end of the loose hose goes to a T, with one hose going from the T to a check valve attached to the motor...looks like the valve cover is the source of the vacuum? Any suggestions on where the other end that's hanging loose should go would be appreciated. Shoulld I just cap off the loose hose and see what happens? thanks.

 

Is that line part of the PCV system??

 

Fixed.
I studied the vacuum system in my 2001 Dodge Ram 3500 motorhome which works great and noted there was no vacuum hose where the "mystery" hose was located on the work van 2002 Dodge Ram 3500.
So I removed the mystery hose, capped the hole in the T where the mystery hose had been attached, and now the venting works directionally as it should instead of just coming out of the defrost vents no matter what setting it was on.
In short, som hack mechanic working for the utility from which I bought the van tried something that didn't work out and didn't make it right afterward.
This problem tied me up for about eight hous in total and kept me thinking about it for a few days. I have choice words for that hack mechanic.
My thanks fo HeyYou for suggestions and to my buddy who loaned me his vacuum gauge so I could test the vacuum check valve and input line.