I would concentrate on figuring out why the DME doesn't see the A/C button, or even defrost button?? It still would be nice to know if there is a controller involved with the manual A/C and how it is wired, and if there is a bus involved, any chance you can get a hold of that info ??

What module are you reading to get evap temp etc. ?

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)