Hey guys, after pouring over old forms, decided to just ask my particular question...
This last summer, as I was driving home from work pulling my trailer up a grade, (¾ throttle, 4th gear, 2k rpms probably) my vent fan went to the defrost position. Once I got to the top and let up on the throttle, it came back to face. I had never noticed it before, but I had also never towed with it with the windows up since my AC hadn't worked before. Now, whenever I'm pulling a grade, or mash the throttle for some reason, my vent switch.
At first, I thought I had a vacuum leak, because i had a really unneaven idle, and incredibly low power. After doing some tune up work, i have a perfectly smooth idle, and decent power (haven't gotten to tow with it since doing the work, but cant wait to see how it performs).
I ran across some forums saying that on the early 2nd gens, the wild vent wasn't caused by a vacuum leak, but instead by a lack of a check valve. How do I go about figuring out which it is, so i can fix it?
Thanks in advance!
Courage

P.S. this is in regard to my 94 Ram 2500 360 nv4500 4x4. Not sure if any of that matters...

 

Sounds like the check valve. Likely have to replace it. It should be in the vacuum line coming off the intake and going towards the firewall.

 

The line that goes through the firewall is noted for chafing… could be just enough to make a hole so it leaks, or (like most) all the way through so you have to go on a fishing expedition to find the end.

 

Thanks guys!
I'll check that vacuum line, and if its not that, then I'll ad a vacuum check valve.

 

There was a tsb for the older trucks, You should use two check valves.
https://www.tsbsearch.com/Dodge/24-01-96-REV-A

 

Wasn't there a large GM style check valve that folks recommended to use to alleviate this issue?? Seems I recall seeing that in a long ago post here.

 

There was a larger one and i researched it but couldn't find them anywhere. The part was probably discontinued and they went with the two check valves.