Here's a video I created tonight after getting the last "bug" out of my hvac system on my old dodge. Hope it helps you guys out!

 

Just what I was looking for....

 

Made a sticky for you guys to find easier.

 

I just wanted to add a few things, The earlier rams didn't have the blend door motor they where cable operated. A common fix for the one with the motor is the heater treater.
https://heatertreater.net/

Another issue is bad check valves, There is one on the passenger side port on the kegger and there is another up by the firewall. You can get replacements from napa for around $6. They are identical but you need to make sure of the vac flow direction before you put them on.
https://www.napaonline.com/en/p/NDP7301349

For people with the earlier rams there was a TSB on adding a check valve that you can read about.
https://www.tsbsearch.com/Dodge/24-01-96-REV-A

 

so where exactly is blend door located in the box.

 

Love that fix! At least your model of dodge allows reasonable access to the system. 1998 durango is a completely different story. It seems like every thing to do with the AC system requires dash removal to rectify. Even the fan motor resistor pack requires a dash removal.

 

I bought my D second hand with 15000 miles on it. The diagram you provided was great but it appears someone had already done the fix on mine before I bough it. I wonder if they just woefully under-designed that reservoir?

 

Some folks have added another reservoir as well....

 

I should have tried adding another reservoir first. I ended up buying a new 12 volt vacuum pump and a adjustable vacuum switch. I haven't installed it yet. I may still add the reservoir before I do the pump thing. Who knows, maybe both would work in an over-kill sort of way!

 

I have had this issue where it would not change modes at all. We noticed a sucking sound coming from the dash. Further digging found the mode selector switch is vacuum operated and the ports that are on the back were cracked. We were able to find an old used one that worked just fine. Currently tho, many years later, it seems to have a mind of its own. In cruise control pulling a hill most of the time you will hear and feel the mode switch as if it lost the suction then return when you have crested the hill. And some days it won't change modes at all.