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Discussion Starter #1 (Edited)
Hello!

So one day my a/c just completely stopped working, wouldn't work at all regardless of the settings I chose from the panel.

Disassembled the dash, got the old blower motor out and it wasn't moving very freely, tested it outside the car and it did spin up but was throwing sparks all over the place due to the tracks being pretty worn and it required a lot of voltage to get running, so I replaced it with a brand new spare part. Tested the blower after swapping it in before reassembling the dash and it was working perfectly in all the settings.

Reassembled the dash, went for a drive, worked great and then after 5 minutes it was done again, not blowing any air regardless of the settings.

I'm really confused now, can it be the FSU? At first I ruled it out since the motor should still spin at full blast but it doesn't work at all, telling me it can't be the FSU. Someone mentioned that a battery that's running low could also cause the blower motor to not spin up at all, gonna check the voltage on it tomorrow but don't see how that makes sense since it did work while the engine wasn't running. Gonna see if it decides to suddenly work again if I disconnect and reconnect the battery again.

So is there anything else I should check, I'm kind of baffled by the situation here.
Thanks!
 

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Wingnut
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motor wont necessarily spin at full blast, or at any other speed, if the FSU is defective. CN90, i believe, has a diy writeup on this site pertaining to troubleshooting the FSU if ya search for it, or google it.
 

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I had the FSU fail a few months after blower motor replacement...and both the blower motor and FSU where brand new factory oem Valeo parts. Sometimes stuff happens...glad I bought from FCP Euro, with lifetime warranty. If you search, there is a thread here with tips on how to narrow down if it is an FSU or blower motor failure.
 

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FSU can fail in different modes, not just one.
 

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The fsu is fairly cheap, I bought one on the auction site two years ago, still working, worth a try.
 

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Discussion Starter #6
UPDATE

So I got my hands on another FSU, before installing it I started my car up again after a couple of days and the blower motor started but just gradually got weaker and weaker until dying out completely, it tried starting up again but couldn't.
Swapped in the new FSU, fired the car up again and nothing, just wouldn't work at all. Swapped the old one back in again and once more it started and ran for about 15 seconds until just gradually dying out. The second FSU came from a donor car and I'm not sure if it's good or bad. What should I try now, get my hands on a brand new FSU or try one from an E39 that I know works?

Really running out of ideas here.
 

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Like I said, I would get a new one, they dont cost much and they do go bad at some point anyway, generally. Its a known problem.
 

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Wingnut
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thats telling you that the new (to you) used FSU aint no good. youre basically back to square 1. as stated by 528iAut, get a new one of a reputable brand and try again.
 

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UPDATE

So I got my hands on another FSU, before installing it I started my car up again after a couple of days and the blower motor started but just gradually got weaker and weaker until dying out completely, it tried starting up again but couldn't.
Swapped in the new FSU, fired the car up again and nothing, just wouldn't work at all. Swapped the old one back in again and once more it started and ran for about 15 seconds until just gradually dying out. The second FSU came from a donor car and I'm not sure if it's good or bad. What should I try now, get my hands on a brand new FSU or try one from an E39 that I know works?

Really running out of ideas here.
Sorry, I don't have a link, but there is a thread either her or on bimmerforums with a tutorial on testing the blower motor to determine if the motor or FSU is bad. I went through similar to you and determined it was the blower motor. After all these years, not a surprise they are now failing. This was almost two years ago, and the new Valeo motor continues to run perfectly. I had similar issues of intermittent operation for about 6 months. Very annoying. In my case, when it ran, it ran strongly, other times, not at all. Then it simply refused to run at all. The tutorial gives instructions for how to jumper some pins on the FSU plug (IIRC) that allows you to start the blower motor. In my case, it still would not start, so I needed a new motor
 

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Discussion Starter #10 (Edited)
Sorry, I don't have a link, but there is a thread either her or on bimmerforums with a tutorial on testing the blower motor to determine if the motor or FSU is bad. I went through similar to you and determined it was the blower motor. After all these years, not a surprise they are now failing. This was almost two years ago, and the new Valeo motor continues to run perfectly. I had similar issues of intermittent operation for about 6 months. Very annoying. In my case, when it ran, it ran strongly, other times, not at all. Then it simply refused to run at all. The tutorial gives instructions for how to jumper some pins on the FSU plug (IIRC) that allows you to start the blower motor. In my case, it still would not start, so I needed a new motor
The blower motor is brand new, I'm gonna see if I can find that tutorial. Just got an FSU from a friends E39 where it worked, installed it in mine and absolutely no action what so ever. Guess I can always take a brand new one back if I buy one and it still won't work.

The fuse 28 is working and since I have a pre-facelift E39 there is no fuse 76. I found out that there are 2 relays behind the glovebox near the firewall so I guess I'm gonna check those aswell.
 
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