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Certified humanoid
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Discussion Starter #1
Hi,

I've been having issues with intermittent AC operation on my 03 530i. Every once in a while when I start the car the AC won't come on. It will make a lot of noise but it's barely moving any air, and the air that does move is warm. The dealer that I bought the car from showed me this "trick" to temporarily "fix" it by disconnecting and reconnecting the pusher fan connector, which does work.

Since I'm in Florida this is not by any means optimal, especially with a flaky hood release cable that currently won't allow me to open the hood without help...

From what I've been able to read it might be worth replacing the FSU, but I'd rather not throw parts at it unless I'm somewhat confident it'll help.

Any input? Do I need a new FSU, or is there anything else I could check?

Thanks
John
 

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Is it the AC not coming on or is it air isn't coming out of the vents? What happens when you turn the fan on max ?
 

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Hi,

Any input? Do I need a new FSU, or is there anything else I could check?

Thanks
John
If the FSU has never been replaced, good chance it's the culprit.

Average FSU is <$50 and even if it turns out not being the FSU, it's good to have a spare around when it actually does go.

But the only way to know is to swap and see if problem goes away.

Other AC related items to check are "Freon" level and compressor cycling
 

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Certified humanoid
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Discussion Starter #4
Is it the AC not coming on or is it air isn't coming out of the vents? What happens when you turn the fan on max ?
Both of those. As I increase the fan speed setting it gets louder and louder, but barely any air pushes through. What little air does get through is warm. Once I reconnect the fan connector it goes back to normal operation, cool and strong airflow.

It seems it has a tendency to work fine for some time, then give me trouble for 3-4 starts, and then be fine for a while.
 

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Certified humanoid
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Discussion Starter #5
Average FSU is <$50 and even if it turns out not being the FSU, it's good to have a spare around when it actually does go.
Need to order a hood release cable along with some other stuff anyway, so I'll give a new FSU a shot, they have a Behr one for ~$26.

Thanks!
 

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Need to order a hood release cable along with some other stuff anyway, so I'll give a new FSU a shot, they have a Behr one for ~$26.

Thanks!
Great. Worth to have as a spare anyway just in case. Here's the write-up by CN90 if you need it:

https://www.bimmerfest.com/forums/showthread.php?t=716322

For the benefit of the community, please report back if it worked so others can benefit in the future from your solution to symptoms like those you exhibited above.
 

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Under the lift arms
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12,940 Posts
wait... the aux fan connector...

"which does work"

what does that mean.. the fan works? or when you disconnect the aux fan and reconnect it.. everything works?

Its very easy to trouble shoot..

put guages on the ports.. confirm your PSI
enguage the ac.. confirm the Compressor locks and spins
activate the cabin fan, confirm that the air is coming out the vent

tell me which part is not working
 

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Nuclear engineer
02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
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Certified humanoid
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Discussion Starter #10
"which does work"

what does that mean.. the fan works? or when you disconnect the aux fan and reconnect it.. everything works?
Sorry, that sentence was pretty unclear. I was referring to the "trick" working, i.e. disconnecting and reconnecting the fan gets the AC running.

Unfortunately it's difficult to tell when it'll will happen again, last time was when I was driving family to catch a flight (had to just suffer without the AC that time).

I could certainly pack a multimeter for when it undoubtedly happens again. What should I test, the voltage over the connection points on the connector?

Thanks for all the feedback thus far.
 

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Nuclear engineer
02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
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A Final Stage Unit - FSU - takes a PWM speed signal from the IHKA and produces a quantized fan speed DC voltage.
 

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Certified humanoid
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Discussion Starter #12
A Final Stage Unit - FSU - takes a PWM speed signal from the IHKA and produces a quantized fan speed DC voltage.
Hey thanks for the reply, I'm not sure I follow what this was in reference to?

I currently have a new FSU on its way. I'm thinking I'll swap that in once it arrives.

Since most of the later replies seem to think it's more likely that my troubles are caused by a failing aux fan I'm wondering if there's a god test I could conduct determine if this is the case. With the fact that it resumes operation after reconnecting I'm not even sure how I'd go about testing it...

Thanks
 

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Under the lift arms
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The problem is not the FSu..

your disconnecting the aux fan and reconnecting it? up tucked in the grill, passenger side kindy gill-ish location

you almost sound like you have a computer problem.. you need the problem to occur and then troubleshoot it while its occurring
 

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Certified humanoid
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Discussion Starter #15
The problem is not the FSu..
Bummer, guess I'll be sitting with a spare FSU until it eventually does drop...

your disconnecting the aux fan and reconnecting it? up tucked in the grill, passenger side kindy gill-ish location
Yes, that exact one.

you almost sound like you have a computer problem..
That is not what I wanted to hear :cry:

What just occurred to me is it could be as simple as a flaky/corroded connector. I'll try giving it a good cleaning & dielectric grease and see if that does anything.
 

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Under the lift arms
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put it in anyway.. all you need is a #2 phillips and a strong finger or pick tool.. the fsu is clipped in with a plug in it

Im super confused...

doug your saying the fsu stops the AUX fan when it goes bad?
 

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Im super confused...

doug your saying the fsu stops the AUX fan when it goes bad?
Both of those. As I increase the fan speed setting it gets louder and louder, but barely any air pushes through. What little air does get through is warm. Once I reconnect the fan connector it goes back to normal operation, cool and strong airflow.

It seems it has a tendency to work fine for some time, then give me trouble for 3-4 starts, and then be fine for a while.

There might be 2 issues with OPs post. Aux fan is one thing and FSU is the other.

OP mentions putting the climate control at MAX barely pushes any air through.

So that would mean does the Aux fan stop the MAX climate control air flow when when it goes bad? The Aux fan is at the front of the car, while the vents are on the other side of the engine's firewall side.

Here is a similar discussion where it could even be the AUC sensor or IHKA panel:

https://www.bimmerforums.com/forum/showthread.php?2354122-A-C-issues-AUX-fan

https://www.google.com/search?q=e39+ac+dme+aux+fan&ie=utf-8&oe=utf-8

After nearly 20 years off the product line, plenty of people have had similar issues and posted on various forums these symptoms and solutions. Funny when people think it's the 1st time their situation has happened to any member after 20 years.

It's really up to posters to read all the past postings to determine what is more similar to their situation and go from there.

It's also why I suggested OP post back their solution afterwards, so future readers can benefit from it when in the same situation.
 

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There might be 2 issues with OPs post. Aux fan is one thing and FSU is the other.

OP mentions putting the climate control at MAX barely pushes any air through.

So that would mean does the Aux fan stop the MAX climate control air flow when when it goes bad? The Aux fan is at the front of the car, while the vents are on the other side of the engine's firewall side.
Good observation CSM. You maybe on to something here.

The old software on older E39 97-98 MY didn't care if the aux fan is working or not, the A/C will kick in regardless. Can't say the same with 02-03 MY, the A/C has to see good status from the aux fan in order to turn on. I don't like the later logic it's kind of anal.

With that said I can't answer your question if the aux fan has anything to do with Max control button is pushed. (I kind of doubted)
 

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With that said I can't answer your question if the aux fan has anything to do with Max control button is pushed. (I kind of doubted)
Both of those. As I increase the fan speed setting it gets louder and louder, but barely any air pushes through.
So, the follow up questions to OP would be: Does the vent blow alot of outside air when at MAX fan setting AND the AC is turned off to just vent normal air? Or does air barely blow when AC is off too?
 

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Certified humanoid
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Discussion Starter #20
These are all great questions that I'll keep in mind for next time it happens.

One additional bit of development that may or may not be related, I hadn't noticed it until the past few weeks. The engine is running way too cool. I have been noticing that the oil gauge not reaching vertical for a few weeks and when running test 07 the other day it's confirming that my ktmp is settling around 63-67C. I have a new coolant temp sensor on its way.

At this point I'm looking at:
- Installing new coolant temp sensor
- Installing new FSU
- Cleaning AUX fan connector

Any ideas of which order to do things to maximize chances of finding out the actual cause for any future owners with the same issue?
 
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