HVAC vacuum diagram

Thank you Danny for the speedy reply. Once I get back out to the shop I will use the diagrams you sent and hopefully figure this out now. Thanks again. Two thumbs up for this website and help. Thank you.

Okay. Followed diagrams you sent, everything looks to be correct. When I plug the rubber manifold into the back of the vacuum valve, I hear "hissing". This is a brand new vacuum valve (spent a lot of money for it, hard to find NOS).

So then I blocked every port on the back of the vacuum valve and only plugged in the Source line, still "hissing" sound. I then just plugged in Source and MAX (Blue) in the back of the vacuum valve, still "hissing" and no go.

If I bypass the vacuum valve completely and run a straight line from Source to MAX the vent opens as expected. I am thinking of manually leaving it this way so I at least have MAX A/C in the truck? I know I will not have Def, or NORM, and I might not have heat, but when Winter comes I can manually hook those up and still completely by pass the vacuum valve?

I guess I have a "bad" new vacuum valve? Can the inner rubber grommet in the vacuum valve be lubricated to prevent "leaking" air? Is the rubber just shot? Is there a MacGyver trick to getting the vacuum valve to work again? If not, I can just run the system with this manual setup.

I have included pictures showing the setup. Thanks again.

None of the lines have been replaced, because when I bypass the vacuum valve none of the lines leak, and no hissing. Keeping the rubber manifold disconnected from the vacuum valve and running new vacuum lines directly into the vacuum valve to the rubber manifold; as pictured, vacuum valve hisses.

Also, blocking every port on the back of the vacuum valve except the source, vacuum valve still hisses. But plugging straight into the source port and Into the Blue port on the rubber manifold, no hissing. As pictured.

Thank you all for the input. I have taken apart my old original one, no o-ring, just a rubber pre-molded rotary valve with channels molded in it. It would appear that over time these rubber molded parts shrink and no longer create the vacuum seal needed. That is why I asked if anybody has repaired these. Even NOS will have the same issue, as I have experienced.

These particular 9-port vacuum valves are almost impossible to find new, no third party makes them anymore. Yes, I can find them used, but at this point and time in this project I simply bypassed the vacuum valve and went source to MAX. This seems to fine for me now. The vent works, the heat works, the fan works, etc. I just won't have windshield DEF.

I own a 3D printer, and I have printed rubber parts before. I would love to re-create that internal rotary valve and print it out of rubber like the original. But the channels are amazingly designed, and the mold that made these must have been a great piece of tooling. The other idea I had was a dash mounted assembly, just move the SOURCE to whatever port is needed, manually. But I have way to many projects to even think about this in detail.

Well, thanks again everybody, I took the truck out for a test drive keeping the SOURCE and MAX directly hooked up, bypassing the vacuum valve completely. Worked like a charm. After replacing all the A/C components, I could almost see my breath in the cab.