FYI, I meant to post this up a couple weeks ago, the shop I took this car to when I first got it to have other things repaired, also repairs some other car s I have, my LT1 Trans Am...anyway when I went to pick up the TA from having the transmission rebuilt I told Jack, the owner about the heater issues with the 560SL. He said it sounded like the control unit, and gave me 3 different control units he had to take home and try. Said they should all be good, but were laying on his shelf and he didn't need them at the moment.

Took them home and the first one I swapped in worked like a champ!
Been working great ever since and didn't cost me a dime, now that's Customer Service!! He also explained how to take the control units apart and look for broken solder connections at certain places that are common if I wanted to repair the one I had. I got the back off the bad one but still didn't find anything broke in there, but would have been an easy solder fix it there was at appeared.

Been working great for several weeks now!

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Rob

'87 560SL
'87 Buick Grand National
'79, '89', 99' Anniversary Trans Ams