I have a '93 300E 3.2L and have two working auxiliary fans. They work fine in the "low" mode, but they sporadically turn on and off when they are in "high" mode, and of course, they cause the relay to click on and off up in the fuse box.
What causes the fans to switch to high mode? Whatever that is has the problem. Is it the Radiator Fan Controller/Resistor; For Auxiliary Fan?

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High Speed Fan Power does not use the Resistor.
Also the High Speed Fan Relay System is not activated until a certain set
operating temperature is reached...Usually much higher than Norms.
'With the KO (Key On,Position #2) unplug your temp sensor connector at the [B10/8]the High Speed Fan(s) should come on.
If not you have a problem with either the High Speed Fan Relay itself ,or the CCU [Pushbutton HVAC control unit]

(picture is of high speed fan relay with 30 amp fuse)[Check that fuse]

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'84 300SD sold
124.128

This is the one you disconnect the two pole connector from to test the High Speed Fan System.[with the Key On]
If the High Fans operate then, AND YOUR WATER TEMPERATURE IS OVER THE
SETPOINT,the problem is the Temperature Sensor.

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'84 300SD sold
124.128

Thanks for the input. I'll try that. It has to be a sensor or a relay. I just don't know which one. This will be very helpful.

Unplugged the temp. sensor and the fans worked great without interruption, finally. So now I know what the problem is. The frustrating sound of the clicking relay constantly turning the fans on/off is finally GONE!

Thanks so much! I should have the new sensor today.

AD keeps us all "straight" on Electron matters.

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'84 300SD sold
124.128