OK, we're on the the right track it is definitely a vacuum problem. I put a gauge on the intake manifold with the system off and was around 8. With the system on, sank to 5. I also noticed the "economy" gauge reading close to the red while idling in neutral with the A/C on.
I then removed the main vacuum line from the rear of the intake and plugged the manifold. This left the interior without vacuum feed from the engine. The controls responded in the same fashion. (no response).
I then re attached the vacuum line at the manifold and checked vacuum at the "Y" splitter above the fusebox by the windshield. I also checked the vacuum lines that attached. Surprisingly they are all in good shape and there is ample vacuum at the lines.

I read the post about checking action while the defroster is on, but I am unable to follow. When I push the defrost button the fan goes to high and I get hot air out the vents in the same manner, just more out of the top vent. It seems the side vents are always on, no matter what the combination selected.

So I guess the next questions are;
Where to start looking for a leak?
How many vacuum valve flaps are there?

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1990 190e 2.6 (About to have a Kompressor )