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Old 02-06-2007, 02:21 PM
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Join Date: Jun 2002
Location: Monrovia, CA
Posts: 496
92 300E aux fan question

I recently bought a 92 300E with 117k mi. The car runs great, but I've got a small problem with the aux fans. When I first start up the car from cold, they both come on full speed intermittently, sometimes for just a second or two, sometimes longer, occasionally for 10 to 15 minutes or so while driving. The coolant temp never goes over 80 even when they're not running. What's the most likely culprit? Is there a simple check and/or fix for this?

What is the proper operation of the two fans? When should each come on and at what speed?


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Old 02-06-2007, 02:33 PM
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Join Date: Aug 2006
Location: Houston, TX
Posts: 450
Proper operation, if the same as my '92 300SE is the fans run occasionally when commanded by the A/C system to compensate for a rise in pressure in the condensor. Also will come on around 100C on the gauge in response to high engine temperatures. I'm pretty sure there are 3 stages - low, med, high.

My guess as to why they're coming on randomly, especially with a cold engine is a faulty temp sender for the fans. You can isolate the cause as being the A/C by leaving it off and seeing if the problem persists. If it does, disconnect the wire from the temp sender for the fans (don't know where it is on your car, but I think mine is on the thermostat housing) and see if the problem persists.

Hope this helps.
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Old 02-06-2007, 03:18 PM
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Join Date: Aug 2006
Posts: 141
Auxilary fan

Look for a blue two pole sensor on the head by the intake manifold. It switches on at 110 c and off at 105c it should also disable compressor when fans are on. If A/C works normally when fans are on high speed the relay is stuck on. If I remember correctly the fan comes on if the connector is removed from the sensor.The relay is in the back of the fuse box.

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