Hello, I have an '88 300e and the aux fan will not run when the car really heats up. But when I disconnect the temp switch with the key on, it comes on high. Bridging the connections does nothing, it keeps running on high. When I plug it back up, it won't come on no matter what the temp.

Can anyone help?

lmarty1359
'88 300e
'74 450sl

Trip On for that sensor is 105/107 C .
Are you reaching that temp???

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A Dalton

No, it's really cool but when I disconnect the temp switch, the fan blows high.

That was not the question.
The question is :
Do you realize the high fan does not trigger until 105C ??????????????????????

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A Dalton

I understand. I'm working on the car now and I let it run until the temp was above 105C ... the fan did not come on.

Ok
Take an ohm reading across the sensor pins when temp gauge says 105.

[ sensor unplugged]

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A Dalton

Starting in 1998 MB started using that variable resistance circuit switch.
Most likely that switch is the problem, & yes the aux fan should go to HIGH.

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