[AtomsForLunch]

So my a/c head unit started flickering last fall, and then the A/C stopped working. I bought a replacement head unit and had a local shop program it, but I still don't have A/C! I replaced the FSU to no avail. I can feel cold air being forced into the cabin at highway speeds but the blower does not blow anything at all. Aux fan doesn't turn on at all, but it does appear to want to turn on if I detach and then reconnect the power connector. Will replace it soon.
Where should I begin troubleshooting? Are the Aux fan and blower be connected? or do I have two separate issues?
edit: the car is a 2001 540i Wagon with ~120,000 miles

 

[edjack]

They are not. You fail to identify the car. There have been changes to the aux fan operation.

We can't help unless you ID the car year, model, and mileage.

 

[AtomsForLunch]

Oops totally forgot. It's a 2001 540i Wagon with 120,000~ miles.

 

[edjack]

On your MY, the aux fan is controlled by the engine computer. It gets its input from the temp sensor in the rad outlet, and runs the fan based on coolant temp.

The engine computer tests the fan upon engine start. It spins it momentarily. I'm not sure if it tests on every startup, or just when cold. If it does not spin, I would suspect the fan controller, mounted on the fan shroud. Don't think the module is available separately.

I've not heard of you symptom before. You will need to get this diagnosed with a BMW-specific scan tool.

Have you examined the wiring from the fan to the e-box for opens or shorts? There s/b 12 V between the two heavier wires at the fan connector.

 

[Chedley]

So, why did you replace the a/c head unit and the fsu ?? What was wrong with it ?? Where there any error codes from the IHKA module ???
Did the shop scan the IHKA module for error codes ?? That is where I would or should start, before throwing parts at the problem. This is the module or "computer" that controls the a/c, heating, and all related air temp in the car. It has diagnostic capabilities and will log error codes to tell you what it sees wrong.
And yes you need a BMW specific scanner (such as INPA or PASoft ?) to scan it.

 

[JimLev]

Your aux fan is PWM controller, no fan controller mounted on the fan shroud like the earlier cars used. Your fan controller is inside the fan motor, it gets PWM (square waves) from the DME to control the fan speed.

 

[Goz007]

i will have to check my notes but if memory serves me correctly, im sure theres a way to check the cabin blower fan by powering the blower fan to full speed by removing the FSU fuse & making a wire to bridging two of the FSU's connectors wires(i struck a similar issue to this on an 01 530i a long time ago)in the end the cause of the issue was a faulty wiring plug at the ambiante temp switch under the front of the car, anyway i will dig through my notes & find out the two wires that will give full power to the internal blower fan through the FSU connector wiring(at least then u will know your cabin blower fan is working)

 

[edjack]

This link may help: DIY: Trouble-shooting HVAC Blower Motor and FSR

 

[Goz007]

thanks edjack.....that post is i think were my notes all came from.......read the thread posted above its very helpful.