HVAC Blower Quits Running NOT FSU

[andermic]

My HVAC recently stopped working and I did quite a bit of research and decided that it must be the FSU (Final Stage Unit Resistor). I ordered an OEM FSU (Behr) online and promptly replaced it. Unfortunately it still didn't work. I did some more research and someone suggested to directly connect the power to the blower motor because sometimes it gets stuck. I did that and to my amazement the blower kicked on. I was super excited because it's been pretty hot and muggy around here lately. I then put in the old FSU and it worked... for about 5 minutes till I started driving down the road. It seems to quit after about 5 minutes of driving. So I tried the new FSU and it had the same issues. I did some more research and it seemed that maybe I got a DOA FSU and that I should return it. To test this, I found a friend with an E39 and I tried his working FSU. I was only able to drive around for about 10 minutes, but it worked. So I ran over to the dealership and picked up an FSU (Sitronic) from the dealer. I installed it and started my drive home and again, to my surprise, it started working fine.. until I was almost home. It stopped working again, but this time about 15 minutes into the drive.

So at this point I have no idea what can be. I'm $200+ into non-returnable FSUs since it's an electronic part.

Symptoms:

When I start the car, the blower and AC work perfectly fine right away. Blows strong, crisp, beautifully cool air and all of the levels work as they should. After about 5-10 minutes is shuts down and blows very softly and eventually completely stops blowing. If I completely turn off the HVAC for a few minutes, it'll blow fine when I turn it back on. However, it stops fairly quickly, after only a few minutes. If I directly wire the blower motor it appears to run for as long as I have it connected.

Any idea of what else could be causing this? It seems to me that something might be over heating, but I literally have no idea anymore.

[cnn]

Since the FSU is new from dealer, the other possibility is a bad HVAC Panel.
About $60 on ebay.

[jneumann]

Since the FSU is new from dealer, the other possibility is a bad HVAC Panel.
About $60 on ebay.

Any differences between years? Any other possibilities if that doesn't change anything?

[cnn]

I think PN 64116901628 is good for all E39's.

[White94RX]

blower motor intermittently failing. I don't think i've ever replaced an IHKA for the problem you describe.

[JimLev]

Connect a meter to the input signal from the HVAC panel to the FSU. See if you still have voltage going to the FSU when the blower motor stops or if you loose the signal, which will stop the blower motor from operating. The control signal to the FSU is at pin 3 blue/red wire) at the FSU connector, referenced to ground, pin 4 brown wire.

[pshovest]

Interesting that fan runs for a while after you fiddle with the FSU connector/wiring.

White94RX,
Do you replace many blower motors in Bimmers? We don't hear about many failures.

blower motor intermittently failing. I don't think i've ever replaced an IHKA for the problem you describe.

[andermic]

Connect a meter to the input signal from the HVAC panel to the FSU. See if you still have voltage going to the FSU when the blower motor stops or if you loose the signal, which will stop the blower motor from operating. The control signal to the FSU is at pin 3 blue/red wire) at the FSU connector, referenced to ground, pin 4 brown wire.

Sorry for the delay in my response. I didn't get an email notification.. I thought no one was interested in my post

Is there a range of voltage I'm looking for? Or am I just looking for any voltage at all? Or should I see if it just changes between running and stopping? I'll have to do this tomorrow sometime.. my meter needs batteries..

Thanks for the tips, I'll report back with what I find.

[JimLev]

IIRC correctly it's a 0 to 8 volt DC voltage you are looking for.
0v=no speed
8v=full speed

[andermic]

Alright... I did some science. I jumped in the car and turned it to max a/c and drove around for awhile. Oddly enough, it never stopped working, and this made me very frustrated. So I thought to myself that maybe I should set it to normal operating conditions. I changed the settings to fully auto at 69 degrees (f). Within a couple of minutes it turned off. I noticed two things at this point. 1.) When the blower is set to full, it keeps running and the FSU stays fairly cool. 2.) When the blower is set to a lower level, it gets super hot and eventually the system kicks off. It's hot enough that I absolutely cannot touch it. So then, due to the fact that I am now the proud owner of 3 FSUs, I replaced one while the system was on but failing. It kicked right back on and worked for awhile until the FSU got hot again and turned off.

Lastly, I checked all of the voltages. Everything seems to be set exactly how it should, according to the information in this thread and from what I've gathered reading a ton of other threads.

At this point, my thoughts are as follow:

1.) Is it entirely possible that I got three bad FSUs? I'm really not excited about the idea of buying another one.
2.) Could something in my electrical system be causing the FSU to over heat. Is it designed to turn off if it over heats?
3.) Perhaps I could put the FSU in an ice-bath to keep it cool so I can stay cool. Logic, right?
4.) Anyone interested in buying a 2003 530i M-Sport? (just kidding, kinda)

So... what next? I'm literally clueless at this point. I'm also fairly confident that it's not the HVAC Panel.

[JimLev]

When you were testing the FSU was it mounted in the hole where it's suppose to be located? If not there is no airflow from the cabin blower to cool it, so it overheats.

[andermic]

Well, the problem started with the FSU mounted where it's supposed to be. And it's failed with the new ones mounted where it's supposed to be. This time I did not have it mounted as I was trying to test it. Tomorrow I will mount it and see if it works, though I'm fairly confident it will fail as it always has.

[achlioptas]

Well, the problem started with the FSU mounted where it's supposed to be. And it's failed with the new ones mounted where it's supposed to be. This time I did not have it mounted as I was trying to test it. Tomorrow I will mount it and see if it works, though I'm fairly confident it will fail as it always has.

Did you ever resolve this?

I have the *exact* same symptoms and have gone through the exact same process. I run the blower at the lowest speed (which maximally heats the FSU), while having the FSU's hedgehog part immersed in water to keep it cool. It appeared to run indefinitely. But 3min after the water was removed, the blower motor stopped.

[geargrinder]

5 years, brother. 5 year old threads aren't exactly voted "most likely to get help". And that guy hasn't posted here AT ALL in 3 years, after he sold his car. So, he's highly unlikely to ever see this thread or board again.

Anyway.

I posted something last year or so about having luck with intermittent FSU's by coating the connector pins with dilectric grease. I believe this is because the extra resistance from a poor connection exacerbates the heating of the unit, as well as make the connection points heat up and warp and go momentarily, put those together and indeed there's plausible logic for why it works.

I tried 'better' fancy contact cleaners on the pins BTW with less luck, I theorize this is because the connection metals are still heating up and flexing around too much, and the dilectric grease helps them slide and maintain a contact whereas the lighter contact cleaner is too dry / sticky.... But whatever the reason, it seems to work... you might try it. Just smear a little dilectric on the connector pins w/ a q-tip and put it all back together like factory and see what happens (this all assuming you've got a new / for-sure-good FSU).

[Kirk Anderson]

Well, OP might never see your reply, but I sure did. Thank you, GearGrinder.