The 400E's (E420's) did have issues (melted wiring) with the ballast resistor for the aux fan, when operating the a/c the fans should run at 70% after 225 lbs or higher.

On most MB's after 1988 (up to 1996) the aux fans are triggered at 100% at approx 107C, if the a/c is off. There is a combi relay on that car for the different aux fan speeds.

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