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#1
07-22-2003, 10:57 PM
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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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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 01:11 PM. 
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#2
07-23-2003, 01:13 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
07-23-2003, 01:27 PM
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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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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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#4
07-23-2003, 01:33 PM
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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
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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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#5
07-23-2003, 02:07 PM
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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
07-23-2003, 02:18 PM
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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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1986 300E 5-Speed 240k mi.
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#7
07-23-2003, 09:09 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
07-23-2003, 10:21 PM
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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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1972 220D ?? miles 1988 300E 200,012 1987 300D Turbo killed 9/25/07, 275,000 miles 1985 Volvo 740 GLE Turobodiesel 218,000 1972 280 SE 4.5 165, 000 - It runs!
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