Aux Fan spins in the wrong direction

[danomite]

Hey all,

We just installed a new aux fan unit (the one in front of the engine) on a 2001 Z3 3.0 with the M54 engine, and when we tested it, I noticed the fan spins in the wrong direction! It's pulling instead of pushing! I double-checked it using mine as a comparison, and sure enough, it's turning the opposite direction. The wiring in the harness connector matches up correctly colorwise (brown - blue - black), and there's only one way to connect the fan harness to the main harness.


Has anyone else seen this before? I've seen it on various other fan units for Mercedes, VW, etc., but never on a BMW one.

I'm guessing the wiring is routed incorrectly to the motor, so we should be able to fix by just swapping the wires and reversing the polarity.

Anyone have any insight on this weird issue?

Cheers

[Mr Bingley]

Sounds like a case of reversed polarity to me.

[danomite]

Sounds like a case of reversed polarity to me.

Indeed. It's rotating against the intended direction of rotation...evident by the little directional arrow on the front of the hub too!

We're gonna try swapping some wires to see if that fixes it. If not, this is going back for a replacement, cuz it's definitely incorrect.

First time I've seen this on a BMW fan.

[JoshS]

First time I've seen this on a BMW fan.

Oh I don't know, BMW fans go the wrong direction all the time ... like the ones that like the X6.

[BladeRunner919]

That sucks!

[Tim95M3]

I've seen this before on a few aftermarket brand E46 and E39 fans. Swap wires around and good to go.

[rf900rkw]

Understanding that this is a three wire motor, which wires would you swap, where?

[BimmerBreaker]

Understanding that this is a three wire motor, which wires would you swap, where?

Wondering this myself. Hard to swap the ground and power when there are 3 wires

[rf900rkw]

If I was going to try it, I would swap the blue and brown, high and ground. This would require the out of phase low speed to be cooperative.

[danomite]

Hey all,

I ran several tests on the aux fan today, and found, what I believe to be, the solution. Originally I thought that the High speed function was the control, and the low speed was the flow-through function...but it turns out I read the wiring diagram incorrectly. The High speed is the flow-through function, and is dependent on the Low speed. So, should you ever come across a 'fan spinning backwards' issue in the future (on the three-wire fans), the following should solve your problem:

Brown wire = Ground
Blue wire = High speed function
Black (with blue stripe) wire = Low speed function

*Swap the Brown (ground) wire with the Black (Low speed) wire at the connector. Blue should still go to blue, as it's the flow-through, High speed function.

This will get your fan spinning in the correct direction. However, it does mean that you'll be running a 10g wire (Black/Low speed) to a 14g wire (Brown/Ground)...which could be slightly worrying (we'll be monitoring this during testing next week).

We'll be removing the entire aux fan assembly next week to do some full diagnostics and checking into what's really going on in the motor housing. Stay tuned.



Cheers,
-Dan

[jajou318]

Dan,

Did you de-pin it from the harness and reinstall?