Had that problem with the same symptoms last year on the 1997 C230 (same ACC system, but differnt engine cooling system). Expert identified the problem to be a bad relay controlling the auxilary (engine) cooling fan. The relay is in the engine bay near the cooling fan stuff and is not expensive. Replacing it cured the problem. Good luck.

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Michael

1988 300 SL (5 Speed)
1994 E320 Wagon
1997 C230