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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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  #1  
Old 02-25-2013, 02:29 PM
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bluebee bluebee is offline
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Do we have a DIY for how to build a test jig testing FSU/FSR operation on the bench?

I realize there is Final Stage Unit/Final Stage Resistor (FSU/FSR) information all over the place (see references below) - so - I would like to open this thread solely to discuss one topic - which is:
- HOW TO BUILD A TEST JIG TO TEST FSU OPERATION ON THE TEST BENCH

Here is my first pass, which is likely too simplistic - but I put it out there as a starting point.

QUESTIONS:
Q0: What do the dotted lines & values (e.g., 4.0, 0.35) indicate in the wiring diagram below?
Q1: Would you put 12VDC (40A) across FSU pins 2 (FSU power) & 4 (FSU ground)?
Q2: What unit would you put across FSU pins 3 (fan signal) and 4 (FSU ground) to vary the input signal (i.e., a potentiometer? a voltage source? a current source?)
Q3: What load (resistive or inductive?) would you put across FSU pins 5 (motor positive) & 1 (motor negative)?
Q4: What unit (current or voltage?) should we look for across FSU pins pins 5 (motor positive) & 1 (motor negative)?

See also:
- What is the canonical thread on the BMW E39 FSU/FSR/Blower Motor Resistor (1) and what is the right brand FSR to purchase (1) (2) when your interior heating & air conditioning HVAC/IHKA blower motor goes haywire (1) (2) (3) (4) (5) (6) (7) (8) & how to test the FSU (1) (2) (3) & how to repair your own final stage resistor including an autopsy & wiring diagram schematic (1) (2) and why a bad final stage unit will cause the battery to drain overnight (1) (2) (3) & how to isolate and replace the E39 blower motor (1) (2) (3) (4) (5) (6) & how not to replace the FSU (1)
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Last edited by bluebee; 02-25-2013 at 05:07 PM.
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  #2  
Old 02-27-2013, 08:10 AM
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Many people "repair" their FSU - but how do they know it's working?

Over in this thread, we're discussing what the resistance & voltage values an FSU sees:
-> E39 (1997 - 2003) > Detailed step by step diagnostic DIY ... dead battery ... parasitic current drain

We've come to the tentative assumption of this basic operative test:
FSU BENCH TEST
  • Remove the FSU from the vehicle
  • Connect a 12VDC (>30 amp) battery to FSU terminals 2 & 4
  • Connect a 10A ammeter in series with a 0.5 ohm to 2ohm 20 watt resistor across FSU terminals 5 & 1
  • Vary the DC voltage from 2 volts to 7.8 volts across FSU terminals 3 & 4
  • Observe the current in the ammeter as you vary that voltage
A key question is whether or not we should be observing the blower motor current or votage, so, I ask:

Q: What determines the blower motor speed? (current? or voltage?)

The reason I ask is because we need to know WHAT to measure at the blower motor terminals.
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  #3  
Old 03-25-2013, 10:56 AM
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Some ideas that came about for TESTING the FSU are the following:
  • It might be the DC blower motor drawing more current over time that is destroying the FSU's, perhaps, instead of the FSUs themselves, failing on their own merits
    • Testing blower motor current over time would be a key step.
    • We can measure in situ motor current either at the battery terminal or across the hard-to-access fuse F76 (perhaps by wiring up a spare blown F76)
  • It could be that temperature cycles are cracking the solder joints
    • We might be able to add temperature sinks; but it wouldn't be easy
  • Some say high current draws from the motor could be spiking the transistors in the FSU
    • Some say a quick-blow fuse in the motor circuit might alleviate that problem
The reasons for the 40 amp fuse F76 are said to be:
  • The motor draws something like 6 Amps running x 12VDC; that's 72 Watts; but the reason you have a 40 Amp fuse is you have very high current start-up transients.
  • One way we can test motor draw is to put 12 volts DC at the FSU harness connector with an ammeter in series (or at the battery).
The reasons for the linear controller (versus PWM) are apparently:
  • The benefit of PWM is that you have full voltage full power available in each pulse so you can start and control a motor with high torque at low rpm
  • PWM control of the fluctuating magnetic fields in the motor coils would cause it to vibrate and make a humming noise at the pwm control frequency, whereas linear control is silent at low speeds.
  • However, PWM increases the need for shielding and filtering radio EMI, especially for the AM bands.
  • Increasing the PWM frequency to 16 K to 22 K would lower the noise but heat up the motor so that's another reason to use linear control; adding an integrator after the PWM would increase the cots of the unit.
  • However, integrating the PWM isn't as good as smoothing the shoulders to get the harmonics down - but again, designing that would cost BMW money.
  • A linear controller will get hot when running the motor slower because of the greater voltage drop across the unit; that's why pwm is the better solution - the semiconductors are either fully on [minimal heat dissipation] or fully off [minimal heat
    dissipation]. The only time they get to dissipate heat is during switching which is a sub-millisecond event and a tiny percentage of the base time.
  • Some say PWM would allow for variable speed, but a DC motor is an inductive load and is not sensibly controlled by such a system unless there is something like a flywheel diode in the circuit to allow the peak voltage (inductive kickback) generated by the motor at pulse cut of to be shunted to earth.
See also:
- How to repair your own final stage resistor including an autopsy & wiring diagram schematic (1)

Note: The Elmos E 10901D appears to be a wide range temperature compensated automotive voltage regulator, specifically designed for an Elmos Semiconductor AG customer.

Quote:
At a guess, one or both of the big power transistors that are inside the FSU are failing. If the failure is that the blower motor doesn't run at all, they are probably failing open. If the failure is either that the blower motor runs at maximum speed, or a fuse blows, then they are probably failing shorted. The blower motor probably draws more current as it ages, and it may eventually be exceeding the power-handling capability of the transistor(s). When the motor is switched off, it may also generate a bit of a voltage spike, which may be above the voltage rating of the transistor(s).

A possible solution is to replace the transistor(s) with ones with a higher power rating in the same package. Another approach is to improve the heat-sinking, maybe by adding metal to the existing fins. Or, cut off the existing fins, bolt it to a huge slab of metal, and relocate the entire thing away from the blower duct.

As a crutch, you could drop the voltage to the FSU a little bit. This would slow down the blower, but also might tend to keep the voltages and currents down to what the transistors can handle. You would need to know the maximum current you would expect the FSU to draw; this probably happens when the charging system voltage is at is maximum, the blower motor is stone cold, and you turn it from "off" to "max". Then, buy a big rectifier diode with a rating of a few amps more than that, and splice it in to the power wire to the FSU. This will drop the voltage by a volt or two all the time. Or, you could put a power resistor in line instead; this will cause a variable voltage drop depending on how much power the FSU and blower is drawing at the time.

Keep in mind that in the winter, keeping the windshield clear is a safety function, so don't drop the blower speed too much.

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

The tricky part depends on the nature of the control signal to the FSU. If it's a simple analog voltage, that is easy to generate on the bench with a potentiometer. If it's some kind of digital bus (CAN?), it is *possible* to generate that on the bench, but it's probably easier to get the dashboard heater control out of a junked car and let it generate the signal.

To load the FSU, you can either use a power resistor that draws about the same amount of current as the blower motor on "high" (a headlight lamp might qualify), or an actual blower motor. The resistor will be "better behaved" than a real motor.

For a power supply, it depends on how much current the blower motor needs. You can get relatively inexpensive 13.8-volt power supplies in ranges up to several amps, designed for running "12 V" equipment on the bench. Samlex is one manufacturer but there are others. If it needs more than 10 A or so, it's probably cheaper to just use a real car battery and charge it when it's not being used.

You should probably arrange it so that there is some air blowing on the FSU under test. If you are using a real blower motor, you can make a duct out of cardboard. If not, use something like a 12 V computer case fan to move a little air across the FSU.

It may also be interesting to have some kind of thermometer on the FSU case while it is under test.

A good way to figure out what the FSU is actually doing is to probe a working car with an oscilloscope. This will show you immediately how the FSU is controlling the blower motor speed, as well as what the control signal looks like. You can stick a straight pin *through* the wire insulation as a test point, and then seal up the hole with electrical tape or silicone sealant.

As has been mentioned, it would be also interesting to cut one of the blower wires and measure the current drawn by the blower motor. For extra credit, do this on a new car (or a newly-installed blower motor) and then compare to a blower motor in a car that has just had its FSU fail.
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Last edited by bluebee; 03-25-2013 at 06:10 PM.
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  #4  
Old 03-25-2013, 12:39 PM
edjack edjack is offline
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This is a waste of time, IMHO. We all know the symptoms of FSU failure. If we observe one or more, just replace the device.

Besides, the early FSU was potted in an epoxy, rather than silicone, making repair almost impossible.

How many of us have bothered to test the thermostat on an engine that won't come up to operating temperature?

There have been very few failures lately, perhaps due to the fact that the FSU has already been replaced by the updated unit in many cars.

Maybe we should ask those with recent failures whether the original was the old style? The original had 13(?) heat sink spikes, thicker than a wood pencil. The current device has 33 (39?) slender, sharp spikes.
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Last edited by edjack; 03-25-2013 at 12:43 PM.
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  #5  
Old 03-25-2013, 06:24 PM
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Quote:
Originally Posted by edjack View Post
just replace the device.
99.9% of the people out there replace their FSU and they're done with thinking about the problem.

[Same thing with people who have a bad DISA, or a bad Behr expansion tank, or a bad ABS control module. They all simply R&R without thinking any further about it.]

Nothing wrong with that - but this thread is trying to get to the ROOT cause of the failure.
As such, this thread isn't a REPAIR thread - but an intelligent discussion of:
  1. How does the FSU work?
  2. Why did BMW design it that way?
  3. What is causing the FSU to fail? <=== more detailed than just "heat"
  4. Is there a way to prove that failure mode (by testing it)?


Quote:
Originally Posted by edjack View Post
the early FSU was potted in an epoxy, rather than silicone, making repair almost impossible.
I think U-N-D-E-R-S-T-A-N-D-I-N-G what is going on is much more important, for the purpose of this thread, than actually repairing the FSU (especially since there are already excellent threads on how to repair the FSU).
However, having removed the "stuff" in the early FSU, I wouldn't characterize it as silicone (see my picture below from my unpotting DIY):
- How to repair your own final stage resistor (1)


Quote:
Originally Posted by edjack View Post
How many of us have bothered to test the thermostat on an engine that won't come up to operating temperature?
As I said, 99.9% of the people will just replace it; so the answer is probably 0.1% of the people will bother testing the thermostat, as shown in this thread:
- How to test the temperature of the coolant when the thermostat opens under normal conditions (1)


Quote:
Originally Posted by edjack View Post
There have been very few failures lately, perhaps due to the fact that the FSU has already been replaced by the updated unit in many cars.
How do you know that?

I've asked and found the exact opposite of that statement, in that we still don't have any convincing evidence that the dealer FSUs last any longer than any other FSU:
- What is the right brand of FSR to purchase & where (1)

Certainly, "I" personally have had both the older (GKR) FSU and the newer (acm) FSU fail on me (see the re-used picture below of my old and new FSU - both of which failed).


Quote:
Originally Posted by edjack View Post
Maybe we should ask those with recent failures whether the original was the old style?
I've had both the old style and the new style fail on me.

In summary, there is GOOD REASON to ASK what is failing on the FSU and how to test it. For example, it could be that the blower motor is actually what is failing (I'm not saying it is, I'm just saying we should look at that).

Or, it could be that those of us who keep the fan speeds low (like I habitually do), are causing more heat to be dissipated in the FSU than others who might be keeping the fan speed higher.

I don't know. Yet, I don't think anyone else knows either.
Hence the need for a thread, such as this one, where only 0.1% of the team will have ideas (while the rest won't care for the question).

Quote:
Thank you very much for your interest in our products.
Unfortunately we are strictly not allowed to provide any information concerning the E109.01D to you as this product is customer specific.
Best regards,
Sina Staufenberg
staatl. geprüfte Betriebswirtin (Recht)
[/quote]
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Last edited by bluebee; 03-25-2013 at 06:34 PM.
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  #6  
Old 03-26-2013, 03:07 AM
JimLev JimLev is offline
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My original 13 spike FSU was replaced twice under warranty, so the car had 3 FSU's. When the 3rd old style failed i replaced it with the new design FSU. That was 8-9 years ago, it is still working. One thing not considered in your post is how many did not use OEM units, the eBay ones are junk.
Your diagram about testing it is correct, however a bad one can work fine until it gets hot enough for the IC chip to fail. Control voltage is 0-8 VDC.
The load resistor should have a metal case mounted on a heatsink to dissipate the heat if you are going to run the test more than a few minutes.
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  #7  
Old 03-26-2013, 09:02 AM
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Quote:
Originally Posted by JimLev View Post
My original 13 spike FSU was replaced twice under warranty, so the car had 3 FSU's. When the 3rd old style failed i replaced it with the new design FSU. That was 8-9 years ago, it is still working.
This disproves the theory that the blower motor is aging and thereby causing the failures.

As far as I can tell, the 16-pin surface mount chip is a (supposedly) robust temperature compensated voltage regulator, and we've been told that the two "bridge" looking things are a simple two-resistor voltage divider.

We've also been told there isn't a square wave anywhere on the board, so it's not pulse-width-modulated circuitry, but linear circuitry.

Quote:
Originally Posted by JimLev View Post
One thing not considered in your post is how many did not use OEM units, the eBay ones are junk.
Unforunately, while I'd "like" to think there is a reliable supplier (in this case, the dealer), we did research what they're selling over in this thread - but there has yet been no clear pattern as to the "right" FSU, dealer or otherwise:
- What is the right brand FSR to purchase (1)

Quote:
Originally Posted by bluebee View Post
Q: Did we ever conclude which BRAND of FSU to buy (not supplier - but BRAND)?

My ACM Germany FSU, that I had replaced on 2/2/2009, apparently suddenly died yesterday (gory details over here):
> E39 (1997 - 2003) > In progress: Step by step diagnostic DIY ... dead battery ... parasitic battery drain

I called a few of the BMW dealers nearest me to figure out what brand Final Stage Resitor they currently sell for my 2002 525i:
  • BMW Fremont 888-208-9746x3
    • Spoke to Troy: He sells the Valeo (which was in stock for $160.04)
  • BMW Mountainview 877-845-1713x3
    • Spoke to Phil: He sells the Valeo (which was in stock for $167.11)
  • BMW East Bay 888-201-2549
    • Spoke to Todd: He sells the Valeo (which was in stock for $144.46)
  • BMW Monterey 866-748-5449 (aka BMW Seaside 831-899-8467)
    • Spoke to Steve: He sells the Valeo (which was in stock for $154.68)
    • He said it lists as Valeo but it says BMW, Sitronic, & Valeo & made in Germany, on the package
  • BMW San Francisco 415-863-9000x1x3x1
    • Spoke to Able: He sells the Valeo (which was in stock for $142.39)
  • BMW Berkeley 800-974-2269
    • Spoke to Guy: He sells the Valeo (which was in stock for $141.22)
  • BMW San Jose 800-298-1501x5x1
    • As usual, the incompetence of BMW of San Jose shined in spades.
    • I won't mention names because they didn't even know what a "final stage resistor" was
    • And, they said they have no way of knowing the brand
    • Whatever it is they sell is $152.98 and they had it in stock.
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  #8  
Old 03-26-2013, 09:27 AM
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Quote:
Originally Posted by JimLev View Post
Control voltage is 0-8 VDC
Do we know this for sure?

Is there a good HVAC control explanation that tells us whether this 0VDC to 8VDC is linear or stepped or pulsed?

Note: In previous posts, "someone" (I don't remember who) said it was 2.0VDC to 7.8VDC.

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Last edited by bluebee; 03-26-2013 at 09:37 AM.
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  #9  
Old 08-10-2013, 08:42 PM
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To test my vehicle, after having seen this periodic 11 amp battery drain (key out of the ignition) in the past:


I built a test connector out of my old original GKR FSU that I had torn apart previously (gory details here):

So that others can follow and improve on the process, I ungracefully tore down that GKR FSU to the circuit board:

The only thing holding the connector on are the five soldered pins (there are also two thin black plastic tabs which probably were only for seating purposes):

Then I sucked out all the solder in the five pins. The trick is to get all the solder out, which is easy with a butane torch & solder-sucker tool:

Once the solder was removed, I then easily removed the connector from the circuit board using pliers and wiggling just a tiny bit:

Then I pushed three Romex wires into the bottom three pin holes; and another Romex cable (14 gauge?) in the top two pin holes:

The Romex fit so perfectly I didn't even have to solder anything:

The result is that it's much easier (and safer) now to get test leads on the harness connector to the FSU to test out cn90's new diagnostic DIY:
-> E39 (1997 - 2003) > DIY: Trouble-shooting HVAC Blower Motor and FSR
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Last edited by bluebee; 09-08-2013 at 01:21 PM.
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  #10  
Old 08-19-2013, 01:59 AM
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For the record, this was posted to the FSU autopsy thread today:
> E39 (1997 - 2003) > failed blower resistor (final stage resistor) not really dead

Quote:
Originally Posted by MMZ_TimeLord View Post
From the information I have found on various threads and different forums, the ELMOS IC is a linear voltage regulator. So the "Fan Regulator" part description is at least somewhat accurate.
Quote:
Originally Posted by MMZ_TimeLord View Post
All the evidence to date suggests that we can put 12VDC on two of the input pins with 0-6 or 0-7 VDC on the 'control' pin with a common ground with the 12VDC. Any 12VDC motor drawing less amperage than our fan motors SHOULD work as a test load.

Granted this would not duplicate the conditions in the vehicle. To do that, you would need to procure a fan from the salvage yard and use that for your test load and a car battery or car charger for your 12VDC source. Unless you have a 30 or 40 amp bench 12VDC supply just lying around.
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Old 09-05-2013, 01:28 PM
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By way of update, my fourth FSU has been working fine, given that the third FSU lasted only five minutes, and the second FSU all of about two or three years. Many thanks to Max at OEMbimmerparts for refunding the FSU cheerfully.

This thread today made me think of diagnostic tests again, as this user apparently has concluded his blower motor is bad (but I don't see that he's run all the tests that cn90 recommends yet):
> E39 (1997 - 2003) > 2002 BMW 525i, HVAC Blower motor procedure

Quote:
Originally Posted by ramp View Post
Good news, replaced the FSU and checked the 40A and 50A fuse all good. I then checked the old FSU, resistance good at all points. Number 1 pin looks a little hot.

Bad news: I get to replace the blower motor. Is there a procedure for this in the Forum?
BTW, in looking up for that OP how to change out the blower motor:
- How to isolate and replace the E39 blower motor (1) (2) (3) (4) (5) (6)

I noticed that the connector at the blower motor is EXACTLY the same shape and size as that at the FSU. I wonder if they're a one-to-one with the wiring, or, if that's just a coincidence?
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  #12  
Old 09-08-2013, 01:07 PM
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bluebee bluebee is offline
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Location: San Jose, California
 
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The question always comes up how to DIAGNOSE (not just throw parts at) a non-working HVAC system.

To that end, I reproduce these thoughts here ...
Quote:
Originally Posted by bluebee View Post
I'm not the expert; but cn90's thread (already referenced) shows how to test the HVAC controller.

So, I guess, it could be one of these (all of which can be tested):
  1. Final Stage Resistor (final stage unit), blower motor resistor (1) (2) (3)
  2. Fuse F76 = 40A, Heater blower (yellow) [cn90 says it should have 12V when HVAC is turned on][QSilver7 says the heater blower controls the air velocity for the cabin/interior HVAC system.]
  3. Fuse F46 = 15A, Blower relay/Parked Car ventilation/Receiver, parked car ventilation (1)
  4. HVAC controller (see tests) by cn90)
  5. K4 = interior heater blower motor relay (1)
  6. Blower motor (1) (2) (3) (4) (5) (6)
  7. F9 = 15A, Air conditioner, Heated washer jets [JimLev says it handles the heated washer jets and the Check Control Module panel]
  8. F20 = 7.5A, Air conditioner, Heated rear window, Heater, Tyre pressure control system [JimLev says F20 and F105 power relay K201, which itself gets power from F75]
  9. Are there any other related fuses or relays? (1)
See also:
- How to troubleshoot a bad FSU final stage unit (1) and how to build a test jig for your FSR final stage resistor (1)
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Last edited by bluebee; 09-08-2013 at 02:42 PM.
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  #13  
Old 09-08-2013, 08:33 PM
scottjoh scottjoh is online now
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Do we have a DIY for how to build a test jig testing FSU/FSR operation on the b

Quote:
Originally Posted by edjack View Post
This is a waste of time, IMHO.
+1
I have a spare FSR in the garage. If I ever suspect it as being bad I'll just replace it. It's not worth my time to test it.

Last edited by scottjoh; 09-08-2013 at 08:35 PM.
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  #14  
Old 09-08-2013, 10:05 PM
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bluebee bluebee is offline
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Most people don't know much of what they fix. They simply replace parts and move on with their lives. They learn nothing; but their car works. The equation works, for them.

For example, I'd guess that more than 90% of the people who own BMWs don't even post to the forums; they get 100% of their problems fixed by going to an Indy or to the dealer. They learn nothing; but their car gets fixed. To ask a question about the FSU would be a waste of their time.

Of the 10% (or so) who do post to the forums, only about 1 in 100 actually dig deeper in order to add to the knowledge level of the team. The other 99% merely ask their question, fix their problem, and they disappear until their next question arises. For them, giving back to the forum is a waste of time. And learning WHY something failed is also a waste of their time. They also learn next to nothing.

Of the 1% who voluntarily spend the effort to give back to the team, probably something like half of them would just replace the FSU and be done with it.

Yet, something like half would actually be interested in a test procedure, and of that half, probably half of those would actually go to the trouble to depot their FSU and debug what's wrong with it.

To my knowledge, out of the thousands of forum members, only a handful have, for example, depotted their FSU and debugged what is truly going on when it fails. Those people have both learned something, and have added to the collective knowledge of the forum, and to them, I (for one) am grateful.

So, while most people clearly would not bother to learn anything about an FSU when it fails, there are very few self-selected people who actually know something about what they're doing. It's for those people that this thread was written.

The rest won't ever understand why any debug effort is expended for a $100 part that dies only once or thrice in the lifetime of the vehicle.
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  #15  
Old 01-05-2014, 09:09 PM
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bluebee bluebee is offline
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This is useful information posted in another thread today:
Quote:
Originally Posted by JimLev View Post
Did you check for power at the connector?
Red/blue is 12 volts and comes from the fuse F76, 40 amps
Brown is chassis ground.
Black/green and red/green go to the blower motor.
Blue/red is the control voltage from the temp control panel, 0-8volts.
If you have 12volts connect it and the brown wire to the blower motor wires to see if the blower will run.
If it does, then see if you have power at the blue/red when you turn the blower speed up.
See also:
- How to troubleshoot a bad FSU final stage unit (1) and how to build a test jig for your FSR final stage resistor (1) & how to autopsy or repair solder cracks in your blower motor resistor (1) & how to replace your HVAC blower resistor (1) (E46) & what FSU is the right one to buy (1)
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Last edited by bluebee; 02-01-2014 at 06:39 PM.
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blower motor resistor, blower resistor, final stage unit, fsr, fsu testing


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