We after scouring the forum for vac leak info I found the TSB on adding the check valve to the climate control tube that goes into the firewall. I'm certain I installed it correctly, and I still have wild vents in 4th and 5th gear.
Would it be safe to assume that since the check valve is in place between the firewall and the elbow that I've isolated the leak down causing the default defrost, to the climate control system? That would mean somewhere in the dash a leak is to be found? It makes sense to me but I'd like someone to back me up on this! Thanks folks!

 

Do you have cruise?
I've heard of them going out by the cruise control module before...

 

I have cruise and I pulled the hose on it and just plugged it for now so that I can rule that out. I had really good vacuum at the end of the hose going to cc at idle so I just plugged it off.

 

Maybe it being plugged is pissing everything else off. lol

 

I would think the check valve at the climate control would isolate it from the effects of pluggin the cc module since the check valve should prevent it from losing vacuum from any other supply to the engine compartment components but I may be wrong!

 

I'm out of ideas myself, but I shall leave this one thought: You're working on a Dodge, anything is possible.

 

 

The wild vents issue is annoying as hell no doubt about it. But, after months and months of trying to fix it I gave up. I have no cruise control and the 4wd wouldn't engage (I replaced with a Posi-Lok)...I tried everything posted on this forum trying to find and fix the vacuum leak and finally just gave up. I began to realize that trying to fix it was more annoying (and driving me bat-**** insane) than the actual problem. Having cruise control would be nice, but I can live without and I've learned to accept the vent issue. I am now at peace.

 

I've had an ever increasing issue with the mixer door cutting off the A/C when accelerating.

This evening I was under the hood looking at an install location for a catch-can, and just happened to run my hand along the vac line to the firewall where the A/C lines are.
So happens that the vac line is cut half through against the firewall where the seal has deteriorated.

I plan to try a rubber tube sleeve repair on the weekend.

Anyway, to this thread, it might be a place to check.

 

I just pulled the glove box and found a small canister there that actuates a vent door and and found a vacuum connector that has 4 lines in it. one of which I think is coming from the engine compartment. It has good vacuum there. As good as it is right at the engine so I know I'm getting vacuum into the cab. The other canister was below the middle of the dash and had a red vac line and brown vac line connected to it. I assume that's a second vacuum actuator which I believe is working as well. What I'm not sure about is at the connector. Does anybody have a schematic on the four vac lines in this connector?

Darren270, I agree whole-heartedly. I've been working on this only a few weeks and I'm tired. I feel pretty certain I have a vacuum leak somewhere past where this connector is because, one, I don't know where it goes and two everything seems to be getting vacuum up to where the connector is but who knows!!! I too have the posi and don't care about cruise so maybe I'll be right there with you! Especially now that I need to do a gear oil change on my front diff! It's a small price to pay to own a really great running $3600 3/4 ton beast for hauling wood and pulling a camper! good evening!