Root cause insight into the common BMW blower motor resistorfailures

[Bimmer Owner]

Does anyone have insight into what is the root cause (and repair) of the
FSU failure that plagues almost every 1997 to 2003 BMW?
http://www.bimmerfest.com/forums/attachment.php?attachmentid=126060&d=1194115994

Also, does anyone have an idea HOW TO TEST a "repaired" FSU?

The "blower motor resistor", which also goes by FSR (Final Stage Resistor)
or by FSU (Final Stage Unit), is known to fry itself in almost every single
E46 (3-series), E39 (5-series), and E38 (7-series) BMW.
http://www.bimmerfest.com/forums/showthread.php?t=143393

The problem with replacing this ~$100 part is that the new replacement FSU
fries itself just as often as the old one did, so you end up repeatedly
replacing your fried FSU every few years or so.
http://www.bimmerfest.com/forums/showthread.php?t=528566

That's fine for most people (although the DIY is a PITA) - but I ask
this newsgroup whether anyone has any insight into WHAT is actually
breaking - and - why?
http://www.bimmerfest.com/forums/showthread.php?t=309399

Here is the best (admittedly sketchy) wiring diagram we have so far:
http://www1.picturepush.com/photo/a/12467819/img/12467819.png

 

[jim beam]

Does anyone have insight into what is the root cause (and repair) of the
FSU failure that plagues almost every 1997 to 2003 BMW?
http://www.bimmerfest.com/forums/attachment.php?attachmentid=126060&d=1194115994

Also, does anyone have an idea HOW TO TEST a "repaired" FSU?

The "blower motor resistor", which also goes by FSR (Final Stage Resistor)
or by FSU (Final Stage Unit), is known to fry itself in almost every single
E46 (3-series), E39 (5-series), and E38 (7-series) BMW.
http://www.bimmerfest.com/forums/showthread.php?t=143393

The problem with replacing this ~$100 part is that the new replacement FSU
fries itself just as often as the old one did, so you end up repeatedly
replacing your fried FSU every few years or so.
http://www.bimmerfest.com/forums/showthread.php?t=528566

That's fine for most people (although the DIY is a PITA) - but I ask
this newsgroup whether anyone has any insight into WHAT is actually
breaking - and - why?
http://www.bimmerfest.com/forums/showthread.php?t=309399

Here is the best (admittedly sketchy) wiring diagram we have so far:
http://www1.picturepush.com/photo/a/12467819/img/12467819.png

that looks like a linear semiconductor controller - an incredibly
antiquated concept for a modern car.

old resistor packs for fans were open wire that sat in the fan's air
stream for cooling. they were generally very reliable if their alloy
wasn't too susceptible to salt.

that unit looks like it still sits in the air stream with that honking
great heat sink and i estimate it's trying to dissipate >100W. that can
only mean it's a linear controller because a modern pwm device can
control high motor currents with very little heat dissipation <10W.

bottom line, a linear controller is always going to get hot and end up
frying itself over time. the only thing you can do is either replace it
with another unit that will ultimately meet the same fate, or undertake
a significant modification.

for the latter, you can try putting an even bigger heat sink on it - but
i doubt there's a lot extra room available. you can also "pwm" it. i
built a similar unit to deal with a linear controller over-heat issue on
my 89 civic.

<http://www.flickr.com/photos/38636024@N00/5068043855>
<http://arduino.cc/en/Tutorial/PWM>

depending on how much time you want to spend on a project like that, pwm
can control superbly and offers benefits like motor speed not being so
susceptible to supply voltage [engine idle voltage drop] etc.

the down side of pwm is that it can generate electrical noise. [poor
stereo installations can be particularly susceptible.] the ideal
solution is to implement pwm with "soft switching", but that's getting
quite advanced.

 

[jim beam]

Blower motor drawing too much amperage taking it out.

if it were an adequately designed unit, it should tolerate that and worse.

Change the
blower motor anytime?

analyze the actual problem - don't just waste money replacing stuff. a
$30 dvm will diagnose this for you, and you should already own one if
you have any ambition to repair any modern vehicle.

 

[the will]

Blower motor drawing too much amperage taking it out. Change the
blower motor anytime?

 

[Nate Nagel]

Blower motor drawing too much amperage taking it out. Change the
blower motor anytime?

My thought as well. Have you measured current draw on a new blower
motor and compared it to one that is installed in a car where the FSU
has failed? that would tell you whether there's any merit to this idea
or not.

nate

 

[Scott Dorsey]

My thought as well. Have you measured current draw on a new blower
motor and compared it to one that is installed in a car where the FSU
has failed? that would tell you whether there's any merit to this idea
or not.

My inclination is to do exactly the same thing I do with the cooling system
issues: blame German engineers who seem to believe that their climate is
typical of the entire world.

I don't see why it is so hard to unpot one of these things and repair them
directly, especially if it's a semiconductor failure. Put a bigger transistor
in there.
--scott

 

[jim beam]

My thought as well. Have you measured current draw on a new blower
motor and compared it to one that is installed in a car where the FSU
has failed? that would tell you whether there's any merit to this idea
or not.

for an "engineer", you're simply not of this planet.

 

[Nate Nagel]

for an "engineer", you're simply not of this planet.

Did you have any suggestions for the OP, or did you just show up to
snipe without contributing anything as per usual?

You do know that most electrical/electronic components have a maximum
current rating, yes? And that electric motors tend to draw more current
when the bearings are going or they are otherwise subjected to loads
higher than that for which they were designed? Does any of this sound
remotely familiar to you?

Really, what the will suggested seems to be a logical first step.

nate

 

[jim beam]

My inclination is to do exactly the same thing I do with the cooling system
issues: blame German engineers who seem to believe that their climate is
typical of the entire world.

that's not going to fix it though. and the germans sell a LOT of these
vehciles in the middle east - it's a good deal hotter there than here.
they know exactly what they're doing.

I don't see why it is so hard to unpot one of these things and repair them
directly, especially if it's a semiconductor failure. Put a bigger transistor
in there.

unpotting is a nightmare - it will take much less time to build your own
pwm controller. who knows, maybe you can switch the existing unit???!!!

 

[jim beam]

Did you have any suggestions for the OP, or did you just show up to
snipe without contributing anything as per usual?
<https://groups.google.com/group/rec...c?dmode=source&output=gplain&noredirect&pli=1>

retard.



You do know that most electrical/electronic components have a maximum
current rating, yes? And that electric motors tend to draw more current
when the bearings are going or they are otherwise subjected to loads
higher than that for which they were designed? Does any of this sound
remotely familiar to you?

don't lecture me on electronics nate.

Really, what the will suggested seems to be a logical first step.

if you don't know what the **** you're doing and don't know how to use a
dvm.

 

[Bimmer Owner]

I don't see why it is so hard to unpot one of these things and repair them
directly, especially if it's a semiconductor failure.
Put a bigger transistor in there.

Here are pictures from the last half dozen who tried that approach:
http://www2.picturepush.com/photo/a/12470740/img/12470740.jpg
http://www4.picturepush.com/photo/a/12470742/img/12470742.jpg
http://www2.picturepush.com/photo/a/12470745/img/12470745.jpg
http://www4.picturepush.com/photo/a/12470747/img/12470747.jpg
http://www5.picturepush.com/photo/a/12470748/img/12470748.jpg
http://www2.picturepush.com/photo/a/12470750/img/12470750.jpg

Most who try to unpot fail, mainly due to damage caused to the
surface-mount circuit board during the initial mechanical degooping
step.

Those deft few who avoid knocking off the surface-mount components
with the debriding chisel, are left with a badly bruised board,
where some have said they've resoldered solder cracks (see pics).

One problem with "put a bigger xtor" is that nobody on this planet
has produced a decent circuit diagram of the FSU.

Does anyone here have access to an FSU circuit diagram?

 

[jim beam]

Here are pictures from the last half dozen who tried that approach:
http://www2.picturepush.com/photo/a/12470740/img/12470740.jpg
http://www4.picturepush.com/photo/a/12470742/img/12470742.jpg
http://www2.picturepush.com/photo/a/12470745/img/12470745.jpg
http://www4.picturepush.com/photo/a/12470747/img/12470747.jpg
http://www5.picturepush.com/photo/a/12470748/img/12470748.jpg
http://www2.picturepush.com/photo/a/12470750/img/12470750.jpg

Most who try to unpot fail, mainly due to damage caused to the
surface-mount circuit board during the initial mechanical degooping
step.

Those deft few who avoid knocking off the surface-mount components
with the debriding chisel, are left with a badly bruised board,
where some have said they've resoldered solder cracks (see pics).

if people priced their time and ignored the damage in which attempts to
unpot invariably result, it's cheaper to just buy a new one.

One problem with "put a bigger xtor" is that nobody on this planet
has produced a decent circuit diagram of the FSU.

Does anyone here have access to an FSU circuit diagram?

you don't need it any more than you need the circuit diagram of a chip's
internals - all you need is its function parameters - which you pretty
much already have.

you might be able to pwm the unit itself thus pretty much removing the
heat component thereby prolonging its life [literally] exponentially.

 

[Bimmer Owner]

Blower motor drawing too much amperage taking it out.
Change the blower motor anytime?

This is an interesting approach, given that the vast majority of
bimmer owners do NOT replace the blower motor - they replace the FSU.

While the blower motor replacement procedure is a major PITA, one
'can' test the leads from the FSU harness connector pins #5 and #1
which are power and ground respectively to the blower motor.

Again, we don't have a circuit diagram, but it has been said that
the blower motor takes about 6 amps (variously, depending on the speed)
but it would take a test jig to test that in operation.

To my knowledge, nobody has created that test jig (although I know
of only one attempt, which failed):
http://www.bimmerfest.com/forums/showthread.php?t=678534&highlight=fsu

It's easy enough to test the resistance of the blower motor though,
and those results have come out at about 0.4 to 0.6 ohms.

It would be expensive to change a blower motor on a whim, so, how
would YOU suggest the blower motor be tested in situ?

 

[Nate Nagel]

<https://groups.google.com/group/rec...c?dmode=source&output=gplain&noredirect&pli=1>

link times out?

retard.



don't lecture me on electronics nate.

ooh, or what? ITG gonna kick my ass? Sorry, I'm more interested in
helping the OP than your delicate little feelers.

if you don't know what the **** you're doing and don't know how to use a
dvm.

WTF is that supposed to mean?

OP can dissect the thing all he wants but it doesn't do him a damn bit
of good to know *what* has failed unless he knows *why* it failed.

nate

 

[Scott Dorsey]

It's easy enough to test the resistance of the blower motor though,
and those results have come out at about 0.4 to 0.6 ohms.

Static resistance doesn't tell you anything, but operating current measured
with a DMM would tell you a lot.

It would be expensive to change a blower motor on a whim, so, how
would YOU suggest the blower motor be tested in situ?

I've never tested one, but I put a drop of turbine oil on the motor bearings
every five years or so. I do the same on the window and seat motors too.

I'd imagine if you listen carefully and have good hearing you can tell if the
motor is binding at all, but many people do not.
--scott

 

[Bimmer Owner]

analyze the actual problem - don't just waste money replacing stuff.

That's exactly what we've done - yet - we need help since nobody to
date has figured out HOW to test an FSU that is fried.
http://www.bimmerfest.com/forums/showthread.php?t=678534

Note: It appears to be an active component, but it probably does
dissipate 100W.

 

[Bimmer Owner]

it's cheaper to just buy a new one.

To be clear, that's what 99.99999999% of the BMW owners do.
But that's not the point of this thread.

The point of this thread is to get a handle on WHY they are all
failing.

Specifically, how to figure that out is the question.

 

[Bimmer Owner]

Static resistance doesn't tell you anything, but operating current
measured with a DMM would tell you a lot.

It 'can' be done, but would require a test jig inserted inline
as the FSU is deeply ensconced under the dash while the blower motor
is even more deeply so.

I've never tested one, but I put a drop of turbine oil on the
motor bearings every five years or so.

While that preventive work might be prudent, the sheer effort
to remove the entire dash simply to access the blower motor
would be problematic.

Still, if the problem is that the blower motor is merely using more
current as it gets older, why wouldn't a NEW FSU burn up within a
few weeks of insertion?

 

[Ismo Salonen]

Still, if the problem is that the blower motor is merely using more
current as it gets older, why wouldn't a NEW FSU burn up within a
few weeks of insertion?

If the unit is near its limits it might just get very hot and parts
start aging very fast -> semiconductors will just fail after a little
while. The new unit should fail sooner than the old one but who knows
who soon, maybe after a few years. Peugeot's ( and Citroen) used just
one huge pnp darlington which failed quite often , it was working too
near its operating limits.

(just my 2 cents)
ismo

 

[Scott Dorsey]

unpotting is a nightmare - it will take much less time to build your own
pwm controller. who knows, maybe you can switch the existing unit???!!!

Unpotting is fun, it's a nice change in the day to just sit down for a couple
hours with a dremel tool and a dental pick.

But I agree, building an aftermarket controller replacement would not be
a tremendously difficult thing to do, and it might be a highly profitable
one.
--scott