Not counting the top of the switchover valve (Y7), the ports are numbered top-to-bottom, 1>7 (Y1-Y7). Per manual that would be Y1 dark red to elements for fresh/recirculated air flaps, Y2 medium green and light blue to same as Y1 (only one of the elements though) as well as vacuum reservoir except on diesels, Y3 red and yellow to elements in the footwell, Y4 red and black to element of the center nozzle flap, Y5 red and white to defroster, Y6 medium green to diverter air flap, and Y7 red and light blue to defroster. As you can see, I was probably incorrect in thinking mine had a cap on one port (unless Y2 since mine is a diesel). If yours has the lines or ports plugged/capped then there may be leaking accumulators (elements above) and a PO chose to have fewer vacuum leaks. Can you get air flow from any of the vent outlets? Do you have a miti-vac? If yes to the latter, you can check the accumulators/elements as well as test the switchover valve. Do some searches for the precautions. The "Service Manual Automatic Climate Control Model 124" from MB of North America, Inc. is an excellent soft cover book to own . . .
Steve

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Steve
'87 300TD - 132K - Soon 4-Sale
'84 300D Turbo - 122K - Driving
'77 VW Type II - 77K - Restored
'08 250EX Ninja
English Bulldog (Brier) - My best friend. Passed away 12/02/04 while in my arms.