[cn90]

My FSR finally gave in at 15y/140K, so I took the opportunity to take some photos for those who need to trouble-shooting HVAC Blower Motor and FSR circuit.

In 90% of the cases, the FSR fails.
In 10% of the cases, the HVAC panel fails.

There are 2 ways an FSR can fail:

1. Not working at all (this is my case)

2. Blower Motor running randomly. draining battery.

--------
There are a few good threads on this topic:

Failed blower resistor (final stage resistor) not really dead
http://www.bimmerfest.com/forums/showthread.php?t=309399

Replacing the final stage unit/blower motor resistor (E39)
http://www.bimmerfest.com/forums/showthread.php?t=143393
------

I want to dedicate a thread for Trouble-shooting HVAC Blower Motor and FSR circuit wiring.
I took some photos myself and combined with photos from bluebee.

Once you understand this circuit, and if your FSR fails in the middle of nowhere, you can easily bypass the FSR and still have blower running! It took me a while to figure out this circuitry...

1. Once you pull out the plastic trim panel (slide out, just note the tabs!), and the carpet trim (Phillips screw, note the 2 hooks), the you can see the FSR connector.

2. The diagram in the links above show the pinout for the FSR itself.
To do proper trouble-shooting, you need to draw the pinout for the Connector itself!
See yellow numbering system:

#1 and #5 are Ground (-) and Positive (+) for the Blower Motor.

#2 is hot with 12V all the time (protected by Fuse 76).

#4 is Ground to chassis.

#3 is signal from the HVAC Panel. When you hit the HVAC button increasing the speed of the blower motor, a voltage signal is sent to #3 to the FSR circuitry:

* Note that #2 and #5 terminals in the FSR are connected. So power goes straight from (+) to terminal #5 ---> Blower Motor (+) pin.
* The speed of Blower Motor is modulated via the "ground circuit" or the #1 and #4 circuit: this circuit is modulated by the HVAC signal, the higher the voltage from HVAC signal, the faster the blower runs. In other words, the FSR acts like a variable resistor in a circuit with its resistance (thus voltage) controlled by the HVAC panel. Example:
- Blower Off: #1 and #4 = Infinity Ohms.
- Minimum speed: probably 2-3V feeding the blower motor.
- Max speed: resistor is by-passed, full voltage 12V to blower motor.

Anyway, most cars run on something similar.

3. Pins #2 and #4 = 12V. Note that I set on "Voltmeter".

4. Pins #1 and #5 = 0.1-0.3 Ohms. Note that I set on "Ohmmeter".

5. To see how the HVAC signal works.
- I unplugged the Connector from the FSR.
- Turned on the engine, hit AC button, AC compressor runs, even when the blower motor is not running!
- This is because once the HAVC panel sends the signal to the FSR, all it cares is: a signal is sent, but the HVAC panel does not care if the FSR/Blower Motor circuits works at all!

- Turned off engine, key in position II. Probes in #3 and #4 to see the HVAC signal:
---> HVAC "Off" = 0 V.
---> HVAC Min speed = 2.04V
---> HVAC Max speed = 8.04V

So, now you can see that if you are stuck with a failed FSR, you can easily by-pass it with:
- Jumper in #1 and #4: completing the ground circuit
- Another jumper in #2 and #5, feeding the blower with full 12V, it will run at max speed.
Just remember to remove the jumper wires when you stop.

This is a temp fix until you find the replacement FSR. Good Luck!

 

[bluebee]

Hi Cam,
I'll be your first customer as I always wish to diagnose what's wrong before replacing any parts & I've always asked how to diagnose the FSU:
- Diagnostic hints requested for an FSU

To delve a bit into history, my first hedgehog failed on 03-26-2008, where Doru kindly pointed me to post 138 of the canonical "elvis" FSU thread.
You'll notice, my first request was for a diagnostic procedure (as I strive to never replace things before proving them bad):

before I go out and get an FSU, may I ask if there is a diagnostic procedure for determining why a fan suddenly stops working?

But, apparently, most people "suspect" it's the FSU; they replace the FSU; and then they move on with their lives.
However, I like to diagnose things, so I started trying to figure out how to diagnose it.
When no good diagnostic procedure was forthcoming, I realized most people consider replacing the FSU their diagnostic procedure. If the new FSU works, then they consider the diagnostics done.

However in my case, the new FSU didn't work (it worked for the first five minutes when cold, and then failed when warm). Early on, I tried to figure out a good diagnostic procedure (starting, in post #16 of the canonical FSU autopsy thread (and in post #7 of this related thread); plus, I tried to determine what's the most reliable FSR out there today).

To further understand the FSU, I autopsied mine, and posted the results here:

Since then, I've had two more blower resistors fail on me, with the resulting summary being:

1. The original GKR lasted from 2002 to 2008:
   • Symptoms were the fan just stopped working
2. The acm replacement FSU lasted from 2008 to 2013
   • Symptoms were erratic behavior & overnight battery drain
3. The Valeo/Sitronic/BMW/acm replacement was half dead on arrival
   • Symptoms were it worked for 5 minutes and then quit
   • Same thing, day after day; so I returned it
4. The Valeo/Sitronic/BMW/acm replacement looks the same
   • I haven't put it in yet, as I wanted to fully test the system

Of course, the first thing one can check is the fuse; but bear in mind, that's not as easy as you would like it to be:
And, I checked the 40 Amp yellow Fuse F76:
- What is the secret to removing the diabolical connectors hindering access to Fuse 76

In preparation for a good diagnostic test, I built a sturdy test connector so that we could measure voltages & very high current (up to 40 Amps) safely & easily as detailed in this thread:
- How to build a test jig for fsu parasitic battery drain and HVAC anomaly diagnostics (1)
Note: My meter only goes to 10 Amps (but the test jig can easily handle 40 Amps)!

Here's a picture of my test jig connector:

Full details on how to build that test jig connector are in the referenced thread; suffice to say I tore down my original GKR FSU & sucked the solder out of the five pins to pull the connector off the circuit board and then I put Romex cable into the holes (they fit perfectly). The Romex cables should be able to handle the 40 amps at 12 Volts, if necessary.

Following in your footsteps, with the engine running, and the FSU not installed, I confirmed your observation that the AC compressor starts running (even with the fan off) simply by pressing the snowflake.

Since I wasn't running current through the wires, and to keep resistance low, I did NOT use the test jig above:

Instead of the test jig, I simply stuck nails into the FSU Harness connector, and then clipped my DMM leads onto the nails.

With the key out of the ignition, and the leads in place as shown above, my results were:

• FSU Harness pin #1 to FSU Harness pin #5 = 1.0 Ohms
• FSU Harness pin #1 to chassis ground = infinite Ohms
• FSU Harness pin #5 to chassis ground = infinite Ohms

Note: FSU pin #1 itself has 0.3 ohms to its cooling tines but FSU pin #5 is not connected to FSUcooling tines (1.2MOhms).
​

• FSU Harness pin #2 to chassis ground = 12.41 VDC
• FSU Harness pin #2 to FSU Harness pin #4 = 12.41 VDC
• FSU Harness pin #2 to FSU Harness pin #5 = 0 VDC
• FSU Harness pin #2 to FSU Harness pin #1 = 0 VDC

Note: FSU pin #2 is tied internally to FSU pin #5 (0.4 Ohms between them).
​

• FSU Harness pin #3 to chassis ground = 0 VDC

Then it was time to test the HVAC controller by turning the key to position 2, and testing the voltage from FSU Harness pin #3 to chassis ground:

With the key in position 2, and the FSU not installed, I tested the HVAC controller as cn90 suggested.

1. With the voltmeter on FSU Harness pin #3 and chassis ground, and with the snowflake off,
   • I ramped the indicated fan speed from 0 dots (fan off) to 16 dots (full ramp).
2. Then, I pressed the snowflake to turn it on,
   • and then ramped the indicated fan speed down from 16 dots (full ramp) to 0 dots (fan off).

When I got to the 16th voltage (a full ramp on the HVAC display), I then turned on the snowflake, and counted back down by pressing the fan speed down button, one dot at a time.
Since the voltages were exactly the same, with or without the snowflake, I only show one voltage for each ramp dot in the table below.

• Ignition in position #2; snowflake off (or on); FSU Harness #3 to chassis ground:

• 1. Fan indication @ 0 dots = 0.104 VDC
  2. Fan indication @ 1 dot = 1.996 VDC (delta = 1.892V)
  3. Fan indication @ 2 dots = 2.307 VDC (delta = 311mv)
  4. Fan indication @ 3 dots = 2.621 VDC (delta = 314mv)
  5. Fan indication @ 4 dots = 2.936 VDC (delta = 315mv)
  6. Fan indication @ 5 dots = 3.250 VDC (delta = 314mv)
  7. Fan indication @ 6 dots = 3.540 VDC (delta = 290mv)
  8. Fan indication @ 7 dots = 3.880 VDC (delta = 340mv)
  9. Fan indication @ 8 dots = 4.120 VDC (delta = 240mv)
  10. Fan indication @ 9 dots = 4.430 VDC (delta = 310mv)
  11. Fan indication @ 10 dots = 4.750 VDC (delta = 320mv)
  12. Fan indication @ 11 dots = 5.060 VDC (delta = 310mv)
  13. Fan indication @ 12 dots = 5.380 VDC (delta = 320mv)
  14. Fan indication @ 13 dots = 5.770 VDC (delta = 390mv)
  15. Fan indication @ 14 dots = 6.080 VDC (delta = 310mv)
  16. Fan indication @ 15 dots = 6.320 VDC (delta = 240mv)
  17. Fan indication @ 16 dots = 7.660 VDC (delta = 1.34V)
  18. Fan indication @ MAX AC = ?.??? VDC

 

[mjalloul11]

Thats why using the blower motor at low speed most of the time will burn the FSU.because it will generat a lot of heat resisting and not enough air to cool it down.

Sent from my GT-I9300 using BimmerApp mobile app

 

[cn90]

Thats why using the blower motor at low speed most of the time will burn the FSU.because it will generat a lot of heat resisting and not enough air to cool it down.

I agree but I am not 100% that is the cause. Perhaps we should set the speed at "medium".

 

[jygesq]

my climate control system usaully runs at one bar

I agree but I am not 100% that is the cause. Perhaps we should set the speed at "medium".

My car is 13 years old had one FSU replaced under warranty and I put in second replacement one, three total.

 

[cn90]

Forgot a few photos...

Good FSR: as designed:
* No power to #3
* #1 and #4 circuit open

* With 9V to #3
* #1 and #4 has R = 3.17 kOhm (on 20 kOhm scale)

Bad FSR:

* Even with power to #3
* #1 and #4 circuit still open

 

[cn90]

My car is 13 years old had one FSU replaced under warranty and I put in second replacement one, three total.

Interesting! My factory FSR (it has a mfg date of 1997) failed at 15y/140K, so not too bad at all.

 

[bluebee]

Cn90,
I have yet to put in my new FSU, but, I would like to ask if you can suggest a diagnostic test for my situation?

The symptoms of my old FSU was a periodic 11 Amp parasitic battery drain, caught on camera (key out of the ignition, and the car just sitting there, with me doing nothing but watching):

The new FSU (Valeo/Sitronic/BMW/acu) worked for five minutes, then overheated; each morning, it worked for five minutes, and overheated.

The replacement FSU (Valeo/Sitronic/Bmw/acu) has yet to be put in as I'm trying to diagnose whether it's the vehicle or not.

Do you suggest any other tests for me?

I don't want to go to the trouble that this guy went through:
-> E39 (1997 - 2003) > Defective?

 

[cn90]

bluebee,

My suggestion is to return the bad FSR (hopefully get your money back) and install the new FSR.

For spare, I'd buy a used one from a reputable seller on ebay for $25 and leave it in your glovebox to be used as a last-minute option. With these FSRs lasting from 1 week to 15 years, I'd not hesitate to buy a used FSR for spare.

A good ebay seller is quarrymotusa from Naples, FL, I have bought quite a few things from them. They specialize in used BMW parts and warranty their stuff.

Here you go:

http://www.ebay.com/itm/BMW-HEATER-...i-325i-328i-Ci-M3-E39-E53-X5-X3-/200950734770

 

[bluebee]

I get confusingly different results, on the new replacement Valeo/Sitronic/BMW/acm FSU.

Good FSR: as designed:
* No power to #3
* #1 and #4 circuit open

Ohm reading
Fluke 75 positive lead on FSU pin #1
Fluke 75 negative lead on FSU pin #4
I get 0.598MOhms

Ohm reading
Fluke 75 positive lead on FSU pin #4
Fluke 75 negative lead on FSU pin #1
I get 0.596 MOhms

* With 9V to #3
* #1 and #4 has R = 3.17 kOhm (on 20 kOhm scale)

Open circuit battery test:
Fluke 75 positive lead on positive (+) terminal of the 9VDC battery
Fluke 75 negative lead on negative (-) terminal of the 9VDC battery
I get 8.33 VDC

Ohm reading
9VDC battery positive (+) terminal to FSU pin #3
9VDC battery minus (-) terminal to FSU pin #4
Fluke 75 positive lead on FSU pin #4
Fluke 75 negative lead on FSU pin #1
I get -13.06 MOhms

Ohm reading
9VDC battery positive (+) terminal to FSU pin #3
9VDC battery minus (-) terminal to FSU pin #4
Fluke 75 positive lead on FSU pin #1
Fluke 75 negative lead on FSU pin #4
I get infinite Ohms

 

[bluebee]

I never did get an answer on why my results differed from cn90's, but, the second (my third overall) replacement FSU from Max has been working fine, so, I'm not sure WHY the discrepancy.

I hope others can report THEIR numbers, so we can help everyone, one at a time.

Meanwhile, this thread today made me think that we need to have everyone contribute to this test thread, so we can isolate a bad blower versus a bad FSU or HVAC controller:

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?

Looking to find a blower motor DIY (simply by typing /blower motor F3), I found a bunch, but, one thing I found interesting was that the blower motor connector itself looks EXACTLY like the FSU connector.
- How to isolate and replace the E39 blower motor (1) (2) (3) (4) (5) (6)

I wonder if the two connectors are as simple as a one-to-one on the wires or if the size and shape is merely a coincidence?

 

[bluebee]

cn90,
Do you think my results differed from yours because my 9v battery was too low (it was the only battery I had at the time, and I pulled it out of a very old smoke alarm so it was in the 8 volt range open circuit)?

I never did run the tests using a good 9v battery ... but, the FSU has been working since putting it in the vehicle.

I'd re-run the tests, but I viciously hate removing that FSU!

EDIT: This post, from another thread today, attempts to identify all the failure points for when the blower motor doesn't work:

I ordered a blower motor.

What would be good for you to do, for the team, when you receive your blower motor, is tell us what the resistance is of the motor, when new. Then you can see if that changes, over time.

Also, when you put 12 volts across it, it would be very nice to know how many amps it takes (be careful with your meter as it may well be greater than 10 amps and most meters are rated for 10 amps DC).

What else could be bad?

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)

1. FSR: unlikely because you just changed it, but there are people with FSR problem straight out of the box, especially non-dealer part.
Make sure yours is BMW FSR.

2. Blower Motor itself.
Instead of tearing the dash apart just to look at the Blower Motor, study this diagram:
http://www.bimmerfest.com/forums/showthread.php?p=3887559

And this diagram:
http://www.bimmerfest.com/forums/showpost.php?p=3203133

On the FSR Connector itself, pins #1 and #5 feed the Blower Motor.
Apply 12 V to #1 and #5 terminals and the Blower should run, if not Blower Motor is bad.
(In BMW terminology 31 is usually ground, 15 is positive feed. So ground goes to SW/GN wire, and positive goes to RT/GN wire).

To be certain that 31 (or terminal 1 on the connector) is ground, using a Digital Volt Meter (a few dollars at Harbor Freight), select Ohm-meter setting, connect terminal 1 on the connector and the chassis, it should read 0 ohm.

Also, check if terminal 2 (Fuse 76 circuit) has 12 V when the HVAC button is switched on.

If you solve this problem, then congrats, you are now formally a BMW master electrician hehe!

HTH.

PS: Make sure you don't have a bad fuse: a bad fuse can either fail completely or fail intermittently. Remove the fuse, check and re-insert it.

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)

 

[Bensley]

Hi I have replaced the blower didn't work with the FSR so I did the links to test and worked full speed I then ordered a new FSR and that does not seems to work do I need to buy a few FSR till I find one that work?
I am very impressed by all your threads and I will do my best to contribute as well.

 

[bluebee]

We found out something new about Fuse F28 today!
> E39 (1997 - 2003) > Blower Motor Stopped working? Try This

According to WDS [what fuse F28 does] depends on build date.

A) up to 9/98 build date, i.e. model year 1998, fuse F28 30 amp, supplies the switched power side of a heater blower relay. This circuit supplies power to the FSU.

B) model years 1999 and later, F28 15 amp, supplies the auto transmission control module.

See also:
- One user's attempt to locate, describe, and photograph all fuses and relays in the BMW E39 with a picture of every fuse & relay (1)

 

[mattmont]

My car has had the water control valve replaced I am still having the issue of cold air only in the vents hot air only in the floor & defrost. Is this also a symptom of a bad FSR please help as this is my first bmw and do not know them very well it is a 2003 330 xi

 

[APSXwideband]

My car has had the water control valve replaced I am still having the issue of cold air only in the vents hot air only in the floor & defrost. Is this also a symptom of a bad FSR please help as this is my first bmw and do not know them very well it is a 2003 330 xi

Usual FSU problems are either no air flow at all or intermittent air flow (on and off). I think your is not an FSU issue.

Do you mean only cold air comes from the front vents on the dash and only hot air comes from the floor and defrost? Does that happen during only the cold days when you try to heat your interior?

APSX WIDEBAND

 

[mattmont]

It always blows cold out of the dash vents regardless of temp setting the 2 outer vents are a bit colder than the 2 center and it always blows hot when I turn on the defrost & floor regardless of the temp settings? I have receipts where the previous owner had the AC control valve replaced 2 weeks before I bought it by a import repair shop and when I look at the AC control valve which is what I think is also called the water control valve it looks brand new it's on the driver side inner fender. This is driving me crazy is the AC valve and water valve different items?

 

[APSXwideband]

It always blows cold out of the dash vents regardless of temp setting the 2 outer vents are a bit colder than the 2 center and it always blows hot when I turn on the defrost & floor regardless of the temp settings? I have receipts where the previous owner had the AC control valve replaced 2 weeks before I bought it by a import repair shop and when I look at the AC control valve which is what I think is also called the water control valve it looks brand new it's on the driver side inner fender. This is driving me crazy is the AC valve and water valve different items?

The water valve might be causing this. After you replace the valve, make
sure there is water flowing thru it. It is fairly hard to bleed the radiator system completely on e46s.

 

[doubletrouble]

OK guys, need your help! First, I would like to thank everyone for sharing their knowledge. Has helped me many times in the past. Especially guys like cn90 and bluebee, who go into great detail! I think bluebee's car and mine were built on the same day as they share a lot of the same problems! What I need help with is a parasitic battery battery drain. Have it narrowed down to the FSR. I have a 400ma load on the battery, goes down to 17ma when I remove the FSR. Replaced the FSR about 6 mo.s ago with the ASPX. FSR still runs the blower and operates normal. Since removing it , cut's the drain, one would think that it is faulty? My concern is, with the key off I still get a .085v reading on pin #3 coming from the HVAC control. Does anyone think that is enough to trigger the FSR and generate a 400ma load? Cannot hear the blower running. I should add that the central and remote locks aren't working either, but one thing at a time! Thanks, Mike

 

[doubletrouble]

Anyone??