My aux fan didn't come on a few weeks ago when the a/c was on. I found that the voltage dropping resistor was burned out on my car. It is located on my 86 300E right behind the driver headlights and on the fender. I tested it by jumping across the terminals with two screwdrivers carefully so as to not short against anything else. Replaced the resistor and my fan worked.

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Ron Miller

1986 300E