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Old 08-28-2005, 02:02 PM
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Join Date: May 2005
Location: Prince Edward Island
Posts: 16
Fan keeps coming on

1990 300d,,,,auxillary fan keeps coming on and off when not needed,,,,whats the problem???and can I unhook it??
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Old 08-28-2005, 02:18 PM
dieselbeagel's Avatar
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Join Date: Nov 2003
Location: California
Posts: 334
A couple of things to check...

1) Is ur A/C charged ? If low, it could contribute to the probelm

2) There is a switch at the left front of the car, behind the head light. Connecting the 2 prongs sets the aux fan on. Is that okay ?

3) Check fuses. The fuse box has a diagram on the cover. I may be wrong but I believe it is the left front corner fuse (in the fuse box). Check if that is okay.

4) Faulty aux fan relay? This is located in the secondary fuse box (behind the main fuse box). Looking at the secondary fuse box from the front of the car, It is the 3rd relay from back of the box, in the left most row.
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Old 08-28-2005, 02:25 PM
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Join Date: Sep 2001
Location: central Texas
Posts: 17,277
You have such a new car that I have no manuals on it.. so I am just throwing out some possibilities....

Maybe your car is hooked up so that not just the temperature switch on the R/Dryer turns on the AUX fan... like maybe the engine needing more cooling ?

I sure would not unhook it unless it will come on by itself when the car engine is cold ( not running ) and is risking running down your battery...
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Old 08-28-2005, 02:48 PM
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Join Date: May 2005
Location: Prince Edward Island
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thanks,,,,I'll check these suggestions out,,,
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Old 08-28-2005, 05:08 PM
Join Date: Aug 2000
Location: Holland, MI
Posts: 1,316
In the OM603 86 SDL, the R/D switch or the coolant 105C switch can activate the aux fan.

It might be a marginal 105C temp sensor, grounding and ungrounding the signal to the relay.

Just one more place to check.

Best Regards,
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Old 08-28-2005, 05:09 PM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 20,656
603 guru Dave M/gsxr says that the coolant temp sensor that triggers the aux fan can get flaky. Maybe this is its swan song.

95 S420
87 300SDL
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