As the title states, I’m troubleshooting the infamous A/C vent to defrost problem.

Looked underneath the dash while cycling the climate control *****. No doors move in any of the settings.

Next step is to look at the check valves.

So, after reading the appropriate manuals, there are supposed to be two check valves in the vacuum lines associated with climate control: one nearest the engine on the passenger side and one downstream of that, at a T-junction

Instead of what I thought I’d find, I found what was pictured. I’m not a Ram expert, but Spidey Sense says this isn’t t right.

 

I once had an issue similar to yours, here is the post with pics, maybe it will help:https://dodgeforum.com/forum/2nd-gen...eeds-help.html

 

Appreciate the link. Helped me see what right looks like.

FWIW, unless that ginormous thing in line is, itself, a check valve, I'm not really sure what it is. My sense is that it's supposed to be connected to the vacuum reservoir; I have yet to remove the cowl to check (due to weather).

Curious if anybody here has seen this before or has this device in their engine bay.

 

It's a checkvalve/minor vacuum reservoir. Probably got put on by a previous owner to deal with wild vents.

 

Interesting. Clearly not stock to this vehicle.

That would be consistent with other things I've find in the truck since I've had it.

Wondering if that small line at the far end even connects to anything now...

 

If you vents aren't working, likely that one was supposed to go to the HVAC control head.

 

Here is the vac line diagram.

You can get the right check valves from napa.
https://www.napaonline.com/en/p/NDP7301349

 

Moparite,

Thanks for the drawing. This is the diagram that actually caused me the greatest confusion between what's actually installed in my truck, as seen in the photo in the OP, and what's supposed to be there. On the basis of this diagram, I was about to go in and change out the downstream check valve; I stopped when I noted the reality/diagram mismatch.

Another day of rain is keeping me from pulling the cowl and looking at what's going on there.

@HeyYou, if that mini reservoir/check valve assembly was supposed to help with wild vents, it wasn't working well at all. Have had the wild vent issue since I had the truck, but only recently did the blower doors stop working altogether.

 

Check it and see if the check valve in it has failed.

 

You possibly have other vacuum leaks. After market PCV valves sometimes flow too much air and are an undetectable vacuum leak. Use a Mopar PCV valve. Your cruise control and 4wd could be leaking or your plenum gasket. Start with fixing the broken line you found and test the vacuum reservoir for leakage.