I need some help deciding how to rig a vacuum line after an engine transplant.

In 2011, the engine in my '95 SE hydrolocked (composite intake manifold fiasco) on an out-of-state trip. I had a '96 engine installed and have had relatively few problems. Recently, thought, I noticed that we weren't getting air (hot or cold) out of the dash vents, only the defrost and a little to the floor. I suspect this has been the case since we had the engine transplant -- I just didn't notice.

Apparently, this is the default condition when the vent controller has no vacuum. Sure enough, after poking around under the dash and hood for awhile, I discovered that the vacuum reservoir mounted on the firewall is missing a tube connecting it to a vacuum source. Everything from the reservoir to the vent actuators is sound.

In the '96 (the engine I'm looking at), the vacuum source on the rear side of the manifold (lower right of first picture) has two lines going from it: a large one to the vacuum brake booster, and a smaller one ("accessory" in the first vacuum diagram) to something that I don't know (third picture). In the '95 (second vacuum diagram), the vacuum source is a tree and the accessory line has a check valve in it.

Should I put a T into the accessory line with a branch going to the vacuum reservoir? Should I put a check valve in the line between the vacuum source and the reservoir?

T should work, vents usually are constant vacuum so you may not need check valve. 3rd pic looks like cruise control module.

Thanks for the quick reply, hounddog. I'll go ahead and T in a branch to the reservoir and post results.

Where is those pics is a vacuum line missing?
I looked at them and cannot see anything missing.

If you are having problems with the air not switching from defrost you should verify there is no vacuum coming into the programmer, which to do so you need to open the glove box, and push back the rubber stops so it will open up enough for you to get in behind it, then towards the body/firewall of the car you should see a vacuum hose coming in, attaching to a plastic adapter, then running into the programmer, if you disconnect the black vacuum line from the plastic adapter that leads it to the programmer you should be able to verify if it has vacuum.

See this site for some pics, and better info detailing what I am talking about.
A/C Service Tech Tip: How to redirect the cooled air in late model GM cars

If you can get some better pics showing where the missing line goes I can better advise you how to proceed.

WilliamE, here'* a pic of the underside of the vacuum reservoir, unbolted from the firewall, with the tube missing from the bottom nipple. The tube on the top nipple goes through the firewall to the controller. This car has standard climate control, not electronic climate control, so it doesn't have the collapsing nipple problem described in the link you provided (it doesn't have that particular part). I wasted plenty of time digging around behind the dash before I figured that one out, but once I did, I was also able to verify that I did not have vacuum to the controller. When I worked my way back to the reservoir checking for vacuum and leaks, I discovered the missing vacuum tube.

Long story short, I spliced a tee into the accessory (narrow) tube that goes from the vacuum source on the back of the intake manifold to the cruise control servo, and branched a vacuum line with a check valve to the empty nipple on the vacuum reservoir. PROBLEM SOLVED!

My guess is that the difference in the vacuum routing between the '95 and '96 engines was enough to fool the mechanic doing the transplant into thinking he was done. There were no unused vacuum tubes coming off the engine, and the unused nipple is well hidden on the reservoir when it'* mounted. Anyways, for the cost of a tee and a foot of tubing I've got functioning dash vents and a bit of experience with vacuum systems! These boards have been very helpful, and I appreciate the effort everyone makes to help out. Thanks!

Oh wow, that does look like it was hidden well, great job finding it, and fixing it!
Also thanks for sharing, this may help others in the future that do not have electronic climate control.