Ran a quick errand this morning. By SoCal standards, it was a bit cold out (ok, ok, it was only 53 deg F). Nonetheless, I turned on some heat and got nothing out of any vent other than defrost. Great, got a vac leak somewhere. Took out my Mytvac and tried to apply some vacuum to the hose coming off the intake manifold, nothing. Popped the vac line off the CC servo and applied vacuum there. Pumped up and held. So far the CC side seems good. While looking for a junction I can use to try the HVAC side (without pulling the control panel), I spotted the break in the line before it runs through the firewall. When I redid my cooling system, I trapped the vac line under the coolant junction pipe (Renix closed system). That's where the break occurred. Some heat shrink tubing joined the clean ends back together and BAAAMMM, vents work again. A small victory but still a victory. At least I didn't have to dig out the reservoir, battery tray or other parts to trace the entire line or break out my "smoke machine".

Pic below show the heat shrink on the section that broke (in red).



My "smoke machine"

 

My 01 vacuum tubing is a brittle patchwork at 25 years old, I can only imagine a 37 year old plastic pipe. I would not have considered heat shrink tubing. I was afraid how much heat those tiny pipes could take. On the big pipes I started using fuel line only because I did not have soft flexible silicon vacuum tubing bigger than 1/8 give or take. Even that was difficult because the fuel line has little flex even when warmed in boiling water and I busted it more during install. I finally went out and got some larger dia silicon vacuum tubing and that went much better. Only issue is the soft silicon has a pretty big outside dia for the comparatively small inner dia so it takes up space. Were you able to shrink with something gentler than my heat gun...something like a hairdryer. If so that would seem like a good fix because im sure the proper sized heatshrink slides on pretty easy. How well did it take bends? PS...I like your inexpensive SMOKE machine, unless your using expensive cigars...lol

 

On my Renix, the big tubes are OK so far. I'll likely use some fuel line as well or something if I have to patch/replace one of them. The heat shrink tubing works well on the small lines as long as the two ends are cut clean so they butt together with no gaps. I have a few more "patches" in the vacuum harness running to the EGR.

The cigar was a Rocky Patel Edge Maduro Toro. One of my favs. I used my torch lighter to shrink (almost melt) the tubing. If it's not evenly shrunk, the heat from the engine finishes it off.