Fan Wiring - Wiring Low Speed & High Speed Together
 

Luckily, this isn't a competition against my car, as it is currently kicking my behind, as every area I look has some issue that was left unfixed by the previous owner.

My car has not over-heated while I have been driving it, even on very hot days. However, I noticed while letting it run in the garage the other night that it started to spit coolant out the cap. After digging into the electrical, it was obvious that low speed was not coming on for the fan. High speed works with AC, which is probably why it never over-heated even on the hottest days. I've already done the cooling system maintenance, bled repeatedly etc. Actually when I was bleeding it in the garage is when I first got it to over-heat and spit out coolant.

After much troubleshooting, it was obvious the issue is with the low speed circuit in the fan itself (presumably the resistor), as I get voltage at the low speed wire at the fan connector when shorting the correct terminals on the two stage temp switch on the radiator.

The really frustrating thing is that I just bought this fan as a good used fan, to replace the badly cracked one that came with the car.

Long explanation to ask a simple question: Is there any harm in just rewiring the fan motor to run a single speed, when it needs to run?

Thanks!

The fan is loud on high speed, and it will wear out , it does not really have a 100% duty cycle on high speed, it normally kicks on and off while running the AC so it does not overheat. Id get the new resistor pack its not that expensive..

Dave

Dave - I was under the impression that the resistor pack was only available attached to a $300 new fan assembly. Do you have a link or part number? Thanks!

Darnit I cant find it,,,, Its just a heavy resistor, I swear someone posted the Radio Shack part number to replace the resister. It was either on here or M42.org..

Dave

Here is the resistor pack shown in the 1995 ETM:

http://www.unofficialbmw.com/john/mi..._resistors.gif

The value marked ".7" is most likely 0.68 ohms. I can't vouch for the accuracy of the values: as you might suppose from the ".7", the car was built from another set (or database) of drawings.

I am guessing by counting the wires and speeds that that wiring diagram above is for the interior blower not the aux fan on the radiator. I have the ETM and I don't recall it having any details on the aux fan resistor.

Can you confirm?

Right you are. I'm sorry, I read "resistor pack" earlier, and spaced.

You are after this attached resistor?

http://www.unofficialbmw.com/john/mi...ks_aux_fan.gif

Right pic, wrong link. The link shows the blower motor one again. The aux fan resistor is a cigar shaped thing attached to the fan.

With the number of these that fail I am surprised no one has created a replacement to sell. I knew I should have paid more attention to that EE for non-EEs class I had to take in college many moons ago.

Here is something that might suggest a value. Two 1.5 ohm 50W resistors in parallel (to yield 0.75 ohm) and clamped to a mass of metal, would be what I might try.

Or on second thought, 2 x 1.0 ohm in parallel for 0.5 ohm.

Could something like this be the part? Not quite, but perhaps getting closer.

John - thanks for the help. That part is a bit different than OEM but is probably their solution to the low speed problem. $55 is one expensive resistor. Apparently if they have the only solution you can charge accordingly.

If someone could measure the resistance, you could probably make a repair or make up a replacement for less than half that, including shipping.

I would go take a measurement, but my auxiliary fan has a second low speed winding instead of the resistor.

Here is a thread on teh same issue,,,
http://forum.roadfly.com/threads/169...C-on-fan-fixed

This is the one I used...

Dave - Very good info in that thread. Which one specifically in that thread did you use? There were several listed between the thread and the links in the thread.

The ballast resistor for coil, seems like a good potential option as Rock Auto has that for a whole $1.29, but the sealed wirewound resistors are nice as well.

I used a big wirewound and screwed it to a old Processor heat sync.. with a couple tabs to hold it on the radiator..

Cheers
Dave