We are putting a 1988 760 turbo that we acquired a while ago back on the road. The heater fan makes a noise like a working fan should but there is no detectable air flow out of the dashboard vents and very weak airflow out of the windshield defroster vents (when defrost is selected).

Could the vacuum motors be kaput?

If a vacuum hose is off, would this result in a vacuum leak or is there a check valve too prevent this?

 

These cars have some kind of Vacuum billows that go bad. I had a 1987 740 GLE that had a simular problem. The billows look like 4 or 5 tennis ***** linked together, white in color. When those things go bad, either they crack or some hose that connects them goes bad, they stop air flow to the vents.

The bad think about it is that it's labor intensive. You have to remove the dash and 1/2 the stuff behind it to get to it. Really sucks!

 

most likely not the vacuum canister itself..probabaly broke,disconnected or broken down vacuum hoses or bad diaphragms...