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  #1  
Old 07-22-2003, 11:57 PM
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Join Date: Sep 2001
Posts: 131
AUX Fan problem and resistor question

I have been having problems with my AUX fan not working in both mine and my moms 300e's. I have narrowed it down to the resistors or whatever senses the temperature and tells the fan to turn on. I am attatchign a picture of the resitor from my car (looks pretty bad doesnt it?) and my moms is in similar condition although not cracked and corroded as much as mine. Is there a way to test a resistor without a multimeter? Also, I will probably ordernew resistors to see if that works because I did have mine work for a couple seconds after I bypassed the resistor and let it idle for about 15 minutes to build the heat up enough to trigger the fan so I know the fan works. I also tested the van with a 12 volt battery charger and both work which is nice that I dont have to spend $300 for each fan.

Any ideas on what is wrong? Resistor, turn on circuit? Something else? Any help would be appreciated.

Thanks.
brockley
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AUX Fan and resistor question-resistor.jpg  
__________________
89 300E Pearl Grey Metallic
7 Spoke 16" staggered wheels (SLK)
215/55/16 Hankook Ventus HRII H405 tires
Euro Headlights
Smoked Corners
Smoked red/clear tail lights

1987 300e Black Metallic (mom's car)
8 hole 15" wheels (C Class)
Clear Corners
Red/Smoked tail lights

Last edited by brockley; 07-23-2003 at 02:11 PM.
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  #2  
Old 07-23-2003, 02:13 PM
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Anyone?
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89 300E Pearl Grey Metallic
7 Spoke 16" staggered wheels (SLK)
215/55/16 Hankook Ventus HRII H405 tires
Euro Headlights
Smoked Corners
Smoked red/clear tail lights

1987 300e Black Metallic (mom's car)
8 hole 15" wheels (C Class)
Clear Corners
Red/Smoked tail lights
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  #3  
Old 07-23-2003, 02:27 PM
it leaks, its german
 
Join Date: Mar 2002
Location: raleigh nc
Posts: 1,111
Pop the rear seciont off the top of the fuse box and look for fuses, replace 'em. Bypassing the resistor will simply mean no low speed fans. The resistors are cheap.


Joe
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  #4  
Old 07-23-2003, 02:33 PM
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Posts: 131
Isnt the AUX fan fuse in the main fuse box? It should be fuse D and be red (20A) I believe and Ive already checked that. Isnt the back fuse box just relays?

brockley
__________________
89 300E Pearl Grey Metallic
7 Spoke 16" staggered wheels (SLK)
215/55/16 Hankook Ventus HRII H405 tires
Euro Headlights
Smoked Corners
Smoked red/clear tail lights

1987 300e Black Metallic (mom's car)
8 hole 15" wheels (C Class)
Clear Corners
Red/Smoked tail lights
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  #5  
Old 07-23-2003, 03:07 PM
it leaks, its german
 
Join Date: Mar 2002
Location: raleigh nc
Posts: 1,111
some models have fused relays.



Joe
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Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.
Raleigh NC
919-881-0364
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  #6  
Old 07-23-2003, 03:18 PM
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Join Date: May 2002
Location: Mass
Posts: 1,127
If your setup is like mine, the fan should come on at 110 degrees, or anytime the A/C is operating.

The resistor in your pics just controls the speed (hi/low) at which the fan operates. I imagine it could fail in such a way that the fan would get no power to it. Mine (with green sensor) is supposed to operate at low speed at 105 degrees engine temp, and high speed at 115 degrees.

You can bypass the 105/115 degree sensor (or whatever yours is) by jumping the terminals at the sensor, which is located towards the rear of the head (on the intake side), and it should have a green or blue plastic top.

Try this:
Jump sensor- see if fan starts.
If not, bypass resistor, and see if fan starts.
This rules in the resistor.

I speak like some sort of expert, when in reality I have not yet figured out why my own fan no longer operates at 105 degrees anymore (or even 115 for that matter), though it does operate when I jump the sensor.
Just have not gotten around to figuring it out...

Best of luck.
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  #7  
Old 07-23-2003, 10:09 PM
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Thanks for the info. Ill check out the sensor. As far as the resistor, if it is broken it should stop current flow because I did get the fan to come on for a short period by bypassing the resistor which is what led me to believe that is the problem. I will order new resistors then try that and see if that helps. If not then its on to the sensors.

brockley
__________________
89 300E Pearl Grey Metallic
7 Spoke 16" staggered wheels (SLK)
215/55/16 Hankook Ventus HRII H405 tires
Euro Headlights
Smoked Corners
Smoked red/clear tail lights

1987 300e Black Metallic (mom's car)
8 hole 15" wheels (C Class)
Clear Corners
Red/Smoked tail lights
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  #8  
Old 07-23-2003, 11:21 PM
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Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
The resistor is for low speed. If it is corroded like yours are, you probably have so little current/voltage going through the fan does not run.

Replace it, they aren't very expensive. If you want more fan for the AC, you can just jumper over it, and the fan will run at high speed instead.

The resistor is bypassed in the circuit containing the temp sensor, so the fan runs on high if the engine temp goes up to 212F.

Peter
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