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Radiator fan always on HIGH, regardless of weather or a/c, this is not normal.

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Old 11-14-2007, 07:36 PM
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Unhappy Radiator fan always on HIGH, regardless of weather or a/c, this is not normal.

I want to first start off stating that this problem is not normal. I turn the car ON, and the radiator fan turns on about 5 seconds after the car is started, and stays on the entire time the car is on, it sounds like what it WOULD sound like IF it was a very hot day with the a/c on. But this occurs regardless of the situation, it always turns on, and at full speed.

This has been going on for about 2 months now and I am finally getting around to posting about the problem. If you could imagine, I can't just leave this problem sit before more problems start occurring, so I've gotta figure out the problem soon.

If anyone has any tips at all or knows what the problem is, please let me know on this thread, thanks.

I will make sure that this thread lives until I solve this ridiculously annoying problem.

My car is a 98 W202. Thanks much for reading!

PS, a couple months before this I was having the "EC light on" problem (reset it), if that has any significance at all. Just throwing it out there.
Old 11-15-2007, 02:05 AM
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Sounds like the fan control unit has died. It's located in the LHF between the bumper and wheel. Pull it out and have a look, it's probably full of corrosion.

The default in case of missing signals is to try and turn the fan on full to let you know there is a fault.

Pretty common to see a few failures after very heavy rain
Old 11-15-2007, 02:25 PM
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Originally Posted by Ausmbtech
Sounds like the fan control unit has died. It's located in the LHF between the bumper and wheel. Pull it out and have a look, it's probably full of corrosion.

The default in case of missing signals is to try and turn the fan on full to let you know there is a fault.

Pretty common to see a few failures after very heavy rain
How do I turn the fan on full? not to mention what is the LHF exactly?

Last edited by stevodotorg; 11-15-2007 at 02:38 PM.
Old 11-15-2007, 07:21 PM
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It's right behind the left front headlight, after you remove the left front fender liner.
Old 11-18-2007, 04:23 PM
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You do not need to turn it on full to test it. The constant running is a safety mechanism, the system turns the fan on full to let you know something is not working as it should and to keep the vehicle running and from overheating. The auxiliary fan control unit is a small black plastic encased box with five prongs where the wiring harness plugs in. It has two small metal mounting brackets, one on either side. The MB number is 016-545-9632, you can get the OE version for about $140 online, depending on which MB dealer you go to, it might be higher.
Old 11-19-2007, 06:59 PM
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Originally Posted by EuroPartsAmeric
You do not need to turn it on full to test it. The constant running is a safety mechanism, the system turns the fan on full to let you know something is not working as it should and to keep the vehicle running and from overheating. The auxiliary fan control unit is a small black plastic encased box with five prongs where the wiring harness plugs in. It has two small metal mounting brackets, one on either side. The MB number is 016-545-9632, you can get the OE version for about $140 online, depending on which MB dealer you go to, it might be higher.
This might be far fetched, but worth an ask..

My mother has a 2006 C230 W203, what are the chances of the aux fan control unit being the same one in my car? It would be nice to be able to just do a swap to see if thats the problem or not.

Anyway, I'm going to check out the little box tonight, I'll try to post some details soon, and photos if there is anything interesting.
Old 11-20-2007, 10:13 AM
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Originally Posted by stevodotorg
This might be far fetched, but worth an ask..

My mother has a 2006 C230 W203, what are the chances of the aux fan control unit being the same one in my car? It would be nice to be able to just do a swap to see if thats the problem or not.

Anyway, I'm going to check out the little box tonight, I'll try to post some details soon, and photos if there is anything interesting.
Stevo, The 203 chassis C230 does not use the same aux fan control.

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