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Old 03-18-2017, 09:09 PM   #1
mr.vang
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Aux fan in high instead of low wiring question

So I removed the clutch fan and using the aux fan as a cooling fan. My AC is also removed. I just installed a m42 80 c aux temp sensor but the low setting is not cooling enough for my comfort. I would like the aux fan to turn on high instead of low. I know the black wire is ground but not too sure about the other two. Do i just cut the two colored wires and switch them?



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Old 03-19-2017, 03:05 AM   #2
jhaurimn
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Dont cut the wire. You can open up the connector with a small screwdriver and switch the wires for the high and low speeds.

Or if you want full control over when the aux fan turns on, you can route some wire from the connector, along the engine bay, into the glove box and then to a fog light switch above the radio.

Make sure you double check which wire is actually ground. Cant remember if its the black wire or the brown/black wire.
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Old 03-19-2017, 08:27 AM   #3
mr.vang
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Originally Posted by jhaurimn View Post
Dont cut the wire. You can open up the connector with a small screwdriver and switch the wires for the high and low speeds.

Or if you want full control over when the aux fan turns on, you can route some wire from the connector, along the engine bay, into the glove box and then to a fog light switch above the radio.

Make sure you double check which wire is actually ground. Cant remember if its the black wire or the brown/black wire.
Awesome. Thanks, you saved me from cutting my wires. I'll double check to see which one is ground.

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Old 03-19-2017, 09:18 AM   #4
Todd Black 88
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If you still have the ac button on your dash, just leave it pushed in.

The aux fan is supposed to go straight to high speed when ac is on. Give it a try first.
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Old 03-19-2017, 03:33 PM   #5
YosemiteSam
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Don't switch those wires. If you do switch them, yes the fan will come on high at a lower temp, but then the fan will switch on to the slower speed if the temperature gets hot enough. Also, pretty sure that the green wire is the one you want to leave where it is, not the black one. I don't have a wiring diagram in front of me right now, but I believe that the wire in the center is the common wire in the switch.

Edit: Keep reading, I retract part of this after Tod Black gives us the wiring diagram.
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Old 03-19-2017, 05:14 PM   #6
mr.vang
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Originally Posted by YosemiteSam View Post
Don't switch those wires. If you do switch them, yes the fan will come on high at a lower temp, but then the fan will switch on to the slower speed if the temperature gets hot enough. Also, pretty sure that the green wire is the one you want to leave where it is, not the black one. I don't have a wiring diagram in front of me right now, but I believe that the wire in the center is the common wire in the switch.
If the high doesn't cool down the motor, there will be no use for the low anyway. I just found out the black is not ground, but instead it's for the low. So from your post, the green is ground? Or the black/brown?

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Old 03-19-2017, 05:18 PM   #7
mr.vang
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Originally Posted by Todd Black 88 View Post
If you still have the ac button on your dash, just leave it pushed in.

The aux fan is supposed to go straight to high speed when ac is on. Give it a try first.
I still have the ac button, but i recall reading somewhere that the ac button won't turn on the aux fan if the dryer is removed. My ac components have been all removed.

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Old 03-19-2017, 08:57 PM   #8
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Yeah, if you are going to switch them, switch the black and black/brown. The green wire is either power or ground, but based on bmw's normal wiring, it is probably ground.
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Old 03-20-2017, 11:20 AM   #9
Todd Black 88
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I was wrong, it would only bring on low speed.

Here.
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Old 03-20-2017, 12:52 PM   #10
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There is no ground in those wires. One of them is 12v which they switch between.

On another note, low speed should be more than adequate to cool it. The stock aux fan is probably a bit crap as it is made for a/c not the radiator. I got a $20 e39 fan from the scrap yard and it cools easily on low speed.
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Old 03-20-2017, 03:31 PM   #11
mr.vang
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During idle in outside 63 degree temperature.

This is when the low fan starts to kick in at 80c. Low fan stay on as long as the car stay idling.


After switching the brown/black wire with black wire so the high fan start at 80c instead of low fan.


Fan stay on for couple minutes and stop. It will turn back on after couple minutes of downtime.


After high fan stop


Im my observation, during idling in ~60 degree temp, I found that with the high fan on, the temp needle never goes pass the middle mark. In low setting, the temp needle goes about half way between the middle mark and 3/4 line.

When the car is moving, the fan is never on or should never be on unless the car is overheating due to a bad water pump, air bubble, blown head, ects. The fan only turn on during idling.

With the clutch fan deleted, the car do pick up faster, and less noisy. When the car is already moving (over ~20 mph), power feel about the same.

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Old 03-20-2017, 03:48 PM   #12
mr.vang
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Originally Posted by potatomash View Post
There is no ground in those wires. One of them is 12v which they switch between.

On another note, low speed should be more than adequate to cool it. The stock aux fan is probably a bit crap as it is made for a/c not the radiator. I got a $20 e39 fan from the scrap yard and it cools easily on low speed.
I figured it out after looking at the diagram. No ground but a power source only.

Is the e39 aux fan bigger and push in more air?

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Old 03-20-2017, 03:48 PM   #13
mr.vang
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Originally Posted by YosemiteSam View Post
Yeah, if you are going to switch them, switch the black and black/brown. The green wire is either power or ground, but based on bmw's normal wiring, it is probably ground.
Thank you

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Old 03-20-2017, 03:59 PM   #14
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Exactly the wiring diagram I was talking about. I was incorrect with my first post, switching the wires is definitely the way to do it. The higher temperature switch does not disengage the lower switch, so the fan will just stay on high.
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