jumping the aux fan resistor

[bimmerR75]

Realized i placed this in the wrong thread initially!

Hi There,

New to working on cars in general!

I have come to find out my Aux Fan on my 91 325i is not turning on at all. Spoke to a shop and they suggested replacing the fan all together, but after some research it seems the common answer to fix the issue is to either a) jump the aux fan resistor (located under the license plate area) or b) completely replace the resistor if that fails to work. I've also heard it may be just a blown fused (fuse 19,20) but I am not sure how to tell if the fuses are blown.

Given my luck and skill with anything electrical when it comes to cars I am not sure what "jumping" the resistor means and how you are supposed to do that.

Any advice would be greatly appreciated! In addition, what kind of tool do you need to test or jump the above?

[bimmerR75]

So upon closer inspection, this was in the place of where the resistor should be. Have no idea what the hell this is in terms of wiring but any suggestions on what I should do? I could see a pair of brown and red wires, then this mess connected.

[bimmerR75]

Figuring I could maybe replace it with this, not sure what the process would be though

https://www.amazon.com/BMW-OEM-Auxiliary-Resistor-Repair/dp/B010A9RHAG?ie=UTF8&*Version*=1&*entries*=0

[uturn]

On the radiator there should be a sensor with three wires. Start there to make sure your fan runs on high speed. Bypass that resistor in front to make sure the low speed circuit is good also. Your picture has you already on your second resistor so avoid that brand. I've had bad luck with the cheapo ones also. Spent the coin on the OEM BMW and they are still going strong.

[bimmerR75]

On the radiator there should be a sensor with three wires. Start there to make sure your fan runs on high speed. Bypass that resistor in front to make sure the low speed circuit is good also. Your picture has you already on your second resistor so avoid that brand. I've had bad luck with the cheapo ones also. Spent the coin on the OEM BMW and they are still going strong.

Thanks, to double check, when you say to bypass the resistor, do you mean run a jump between the different wires on the sensor to make sure the fan functions properly?

If thats the case, soon as I make sure the fans motor isn't screwed up, going to get the OEM resistor, just will need to figure out which wires to install it to.

[bimmerR75]

So bypassed the sensor, high speed works, low speed does not but the fuse box clicks. Would that indicate its the resistor and or the relay that needs replacing?

[jeffnhiscars]

If you bypass the resistor then there is no low speed. That's why you up the fuse to 30A. I run all my e30s on high even if the resistors work.

[330SMG]

The wiring is heavy enough for 30 amps. The fastest way to burn up a car is put too large a fuse on too small a wire.
If you have not downloaded a wiring schematic this would be a good idea.

[jeffnhiscars]

The low speed fuse is sized to the design load of the fan at low speed but the wiring is exactly the same .75mm as the wire for the high speed circuit. bypass the resistor and you have to change the fuse or it will just keep blowing.

[jrobie79]

I wanted to chime in on this as I'm having issues myself - I installed a brand new switch, resistor, and radiator sensor when I had my valance off for paint. I verified the fan worked prior to installation, and wired everything up in the stock fashion. Now when my car gets up to temp, fuse 18 keeps blowing, I'm assuming it's when the fan wants to kick on. I was idling in a parking lot, when I saw the temp creep up, and then it started smelling like something was burning - I opened the hood, no smoke, but fuse 18 was popped again. I didn't find any damaged wires, so I dunno what the issue is. Any suggestions on troubleshooting?

[bimmerR75]

The low speed fuse is sized to the design load of the fan at low speed but the wiring is exactly the same .75mm as the wire for the high speed circuit. bypass the resistor and you have to change the fuse or it will just keep blowing.

Gotcha, I determined all the fuses are in tact and not blown, so I am going to try purchasing a new resistor. As I mentioned the relay does "click" so there isn't a power issue in the fuse box, somethings just getting lost between the temp switch and the low speed function of the fan.

Given the relay works, high speed relay/fan function works, I am going to go ahead and assume the low speed resistor is the culprit and pick up one of these.

http://www.pelicanparts.com/cgi-bin/ksearch/PEL_search_2014.cgi?command=show_part_page&please_wait=NA&SUPERCAT_FLAG=Y&make=BMW&model=201&section=ELSWCH&page=2&bookmark=6&part_number=64-12-1-388-069-INT

[bimmerR75]

Thanks for the assistance everyone, replaced the resistor and its working fine now!