Sorry to add to this old thread but I'm desperate. I have a 95' W124 wagon with a vacuum leak. I've located a Red/blue vacuum line in the engine compartment that leaks thanks to the Mity-vac. It branches off the left side of the yellow check valve. The green/yellow line goes in under the dash and feeds the top of the vacuum manifold but what does the red/blue line do? I can't see where it goes from above or under the car. When I plug the left side of my check valve (where the red/blue line goes) all of the vents and climate control work perfect. When I hook the red/blue back up I loose vacuum and I go into default mode with only defrost and side vents. Anybody got a clue??

Please see attached pic.

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