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Old 04-15-2008, 03:57 PM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
Join Date: Mar 2008
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Mein Auto: 02 BMW 525i M54 auto 130K
The next person with a replacement FSU... please compare the old and new electrically

I would be interested in seeing exactly what the differences are between a new and faulty units.
Hi Elvis,
I understand that almost everyone in this thread and elsewhere replaced their FSU whenever anything went wrong, e.g.,

However, some replaced the FSU and the problems persisted, e.g., http://www.*************/forum/e36-3-...stor-help.html

Some said it was the blower motor itself; others implicated the control unit; while none implicated the two sensors in the circuit.

So, it's, uh, well, it's as clear as not very clear. Seems to me, the FSU can't hurt, and, it doesn't cost a lot but, it just goes against my grain to replace without testing first. If I have to buy equipment (within reason) to test the thing, well then, so be it.

The question becomes what to test once the FSU is in our hands. Do we have a WIRING DIAGRAM?
Oh well ... If I end up getting a new FSU (I'll wait to see if it goes out AGAIN), you can rest assured I'll ohmmeter it while both are in my hands!

If the FSU is merely a bank of resistors, we'll see a short or open; if it's a bunch of power transistors, I'm not sure what we'll see ... as we might have to bias the transistors to get it to show it's mettle ... either way ... let's begin to gather the data starting with the very next person who has a bad and good BMW FSU and/or blower motor in their hands!!!!!


Here, by the way, is what a BMW blower motor looks like ...
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Last edited by bluebee; 04-15-2008 at 04:04 PM.