Auxiliary Fan (Compression Shroud) DIY [Air Conditioning]

[bastereo]

That small wire the the speed signal from the computer. The large two are power and ground.

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[Turbo_Bimmer]

Originally Posted by corNIC

Okay I'm talking about that smaller wire on the fan connecter. I can not get this fan to spin even directly connected to my battery like at ALL. However when I try directly connecting the fan to the battery, with that smaller black/green wire plugged into the terminal it will try and jolt it. I'm beginning to wonder if that wire is a ground?

That small wire comes from the DME to control the speed of the fan. The DME sends a signal with a variable duty cycle to vary the speed.
According to the schematic, the output of the DME grounds the small wire through a resistor to drive the base of the PNP transistor inside the fan.
So, if you want to test the fan on the bench, you should apply 12V to the terminal corresponding to the positive big wire, ground to the negative big wire, and ground (continious or intermittent) to the corresponding terminal of the small wire with a current limitting resistor in serie (value around 50 to 100 ohms). If it doesn't turn, try to lower the value of the resistance.
The fan shoud turn. Don't let the fan turn for too long though, the transistor won't be in an correct air flow to cool down if tested on the bench.

[corNIC]

Originally Posted by Turbo_Bimmer

That small wire comes from the DME to control the speed of the fan. The DME sends a signal with a variable duty cycle to vary the speed.
According to the schematic, the output of the DME grounds the small wire through a resistor to drive the base of the PNP transistor inside the fan.
So, if you want to test the fan on the bench, you should apply 12V to the terminal corresponding to the positive big wire, ground to the negative big wire, and ground (continious or intermittent) to the corresponding terminal of the small wire with a current limitting resistor in serie (value around 50 to 100 ohms). If it doesn't turn, try to lower the value of the resistance.
The fan shoud turn. Don't let the fan turn for too long though, the transistor won't be in an correct air flow to cool down if tested on the bench.

This is good information here for me thank you very much. I will perform this test later today if possible and report back with my findings. I would also like to point out there is no way in hell I will remove this fan to test it at this point cause it's awful to get to!

[mysweetx5]

Yes CorNIC! the blk/green wire is a ground, I think all 3 of them came from directly through the fan motor, so meaning there's no such of fuse or relay
that could cut the power from going through, as long you got power at the plug connector head. And were both tried the same
thing by sending a separate power to the fan motor itself, and if you watch closely, you can see the fan blades (jump/jolt) a little bit.

Otherwise, fixing the thermostat will be a good fix for the future winter soon, but will NOT garanteed to fix the fan issue. Because I have my thermostat working great no problem, and I never had any overheated
engine while driving. But my friend who has a jeep cherokee told me that
his auxiliary fan was acting the same way by doing a little jump/jolt when
connected, like it was going to run but suddenly stopped. He than bought
a new fan which worked perfectly. By the way I'm a little curious now bcoz
you claimed having a new fan and it doesn't turn on when the A/C kicks in.

That made me wonder now if I ever buy this expensive auxiliary fan would it be the same for me to not able to turn on when my A/C kicks in???
This fan is like a mystery, where a few cars comes with it, but a few of
them don't have it, and they're still working fine without changing the air
temperature specially when sitting at the traffic or red lights.

[corNIC]

Yes this fan is quite the mystery for such a simple part. I would also like to point out that if the fan connecter on my car is not connected the AC condenser will not even attempt to turn on lol. I agree replacing teh thermostat should not fix this issue. I guess I'm going to also test the voltage on my power leads. I think I am correct in assuming that 12V should always be there even if the small wire is not connected.

[mysweetx5]

Now I'm also requiring about this sensor part pictured below
because a few owner claimed to replace it and turned out to be the issue
And that could be the same problem for you as well. Now I'm just
following another forum on this, to ensure that this is the culprit
that caused my auxiliary fan to not running. If this the case than,
it would be one of the easiest repair than ever because this sensor is
located upfront just above the radiator on the inside, and it this NOT expensive at all.

Otherwise, this aux fan seems not that important on BMW's!
I guess you want to know why I say that?

1-These no such warning light/indication to tell you that aux fan has failed
Ex. check brake light, check coolant level, check fog lamp, washer fluid low

2-Found a few BMW's that comes with it, and some of them don't have it which are the same year/model as well.

(when I tested the head connector that bring the power, YES there's power there even when the engine's not running)

[corNIC]

Originally Posted by mysweetx5

Now I'm also requiring about this sensor part pictured below
because a few owner claimed to replace it and turned out to be the issue
And that could be the same problem for you as well. Now I'm just
following another forum on this, to ensure that this is the culprit
that caused my auxiliary fan to not running. If this the case than,
it would be one of the easiest repair than ever because this sensor is
located upfront just above the radiator on the inside, and it this NOT expensive at all.

Otherwise, this aux fan seems not that important on BMW's!
I guess you want to know why I say that?

1-These no such warning light/indication to tell you that aux fan has failed
Ex. check brake light, check coolant level, check fog lamp, washer fluid low

2-Found a few BMW's that comes with it, and some of them don't have it which are the same year/model as well.

(when I tested the head connector that bring the power, YES there's power there even when the engine's not running)

This has to be it. I have also seen this part on mine as well but wasn't sure. Does anyone know what it is actually called? Going to see if the local store has one and just go ahead and replace this after I test my voltage which i highly doubt is the issue.

[mysweetx5]

i's called Auc sensor (Automatic Recirculated Air Control)

[corNIC]

I'm getting 13.8V to the fan power connector! Next test I guess I need to make 100% sure the fan is still working.

[bugbyte]

Hey CorNic,

Is your Aux Fan problem fixed? My fan never kicks on and I Am also wondering why. No warning light on my X.