When I did my work this weekend, I went to the ProGrama website and clicked on the CCU for my 86300sdl. There was a wonderful troubleshooting guide on how to check the monovalve, the awp, and all of the sensors using a VOM. This was all done by measuring thr resistances at the plug in connections on the CCU wiring harness. It was really easy. Go check their site and it may help you.

I found that all my sensors were within spec and my awp was also within spec. I also applied 12 volts to the awp connector under the hood and listened to my pump run. I found my monovalve ruptured, I found one vacuum pod bad( the one for the center vents) ( man was that a bear to replace) and I found my CCU bad.

I had another in stock in my attic. ( I get them from junked cars in the wrecking yard.) I plugged everything in and it worked.
By the way, I also have a very valuable book that I purchased from Mercedes back in 1990. It is the Climate Control Manual in print. It covers 1981 thru 85 and then revisions for 86,87,88. This book was invaluable for resistance readings specs on the different sensors, and instructions on how to replace the different pods etc..
If you ever come across one on E-Bay, snatch it up!!!

Good Luck and if I can help you somehow, drop me a line

JOhn