I bought a service manual heating air con book for the 123. The thing is dated 1988.
It covers all 3 systems in really good detail. Now I see why every scan of the wiring diagrams suck! Those are the smallest numbers I've ever seen. I swear it's a friggen eye test. Now here is the real pisser. This 80dollar book doesn't mention the Klima relay at all!

So there is no way to see how the Klima interfaces with the rest of the system. What a joke!

Where have all the Benz experts gone around here and BW?? At this point, I'll even entertain a dumb idea! I do know, when someone has this problem in the future, and they will, these threads will prove valuable!

I installed another used temp reg box and now I have the compressor "on" signal at the klima plug. This is proved by having +11vts at pins 5 & 10. Only trouble is I got that with the push button box OFF! So I guess my box needs more work. :-/ Bought another push button box on fleabay. Fingers crossed as I fire the parts cannon at this sob!
And of course the clutch didn't engage. (Klima relay)

Where is my expert here that has built his own KLIMA that works??? Because the 3 boxes I have aren't worth a damn. One of them is going to get gutted for parts thats for sure!

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Got an overhauled box from programa. YGBSM mean anything to any of you??? :-/

https://youtu.be/r638nKSyl-M

Way to stay at it. Someday a future Benzer will be glad to find this.

Well the 2nd box from programa got everything right with the world again. It is currently running with a Klima relay. The pump turns on when it should and my windshield is nice and cold. :-/

Next up, RIP OUT THE DASH!