1990 560 SEC Heating Ac Control Unit

They're different parts. Slightly different shape. Without looking at the schamatics I'd guess electrically they're the same but that is in fact a guess.

NO.

86 up pushbutton unit does not have them externally.

Yabbut ya know what? The facia plate for both has the same part number so I suspect the spacing is exactly the same and knowing Mercedes (and the complexity of those circuits) It wouldn't surprise me if they left well enough alone and that the two connectors actually fit and worked.

Has anybody actually tried this?

I think it depend on the model and the market they were sold in new. I've seen both generations with either system.

He might be right.

Thanx for all your input guys, I was able to find a remanufactured unit out of an 88 for 67.50. Hope this and a new monovalve insert will cure all of my heating and AC problems.