Hi Dave, That is it! No line to the side fitting of the vacuum element pictured. I hooked it up and freed the black vent line.
As an experiment I tried the various climate control settings both with and without the line connected and did not notice any significant difference.
I wonder why a PO plugged it????
Another MB mystery......

And yes, 1985 not 1895. But, just think what it would be worth.

Thank You again,
Ron