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Blower Motor diagnostics

2K views 12 replies 7 participants last post by  bluebee 
#1 · (Edited)
Hello,

My first thread here and I am already asking for help :)

Few days ago the blower motor in my 2003 E39 530i stopped working. I was kind of expecting it as it was squicking for last few months.
It stopped working a day before I was to take the car for an oil change, so when I took the car to the shop, I asked technician to do his diagnosis and to give me a quote for repair (blower motor replacement), telling him that most likely that the blower motor died.

He came back to me with a diagnose that it is not the blower motor but FSU (resistor) which is common point of failure with E39 and he gave me quote for replacement. He said that he did the diagnostics and he was able to turn on the blower motor (!?), which means that the resistor is gone.
He made my day, I thought, knowing that blower motor replacement would make my wallet very light. On the other hand, I can easily replace FSU by myself.
I bought a new genuine BMW FSU, read the DIY and it took me about 30 minutes to replace FSU. With exception of having my 6'-5" body with proportionally long limbs doing all kind of gymnastics under the glove box, things went pretty smooth.
It was the time to celebrate job well done, so I turn the key on but.. nothing... no blowing from the ducts..
I decided to check if the fuse is blown. I found well hidden 40 amp fuse behind the glove box but it was OK - fuse not blown.
Now I am not sure what is going on - the guy in the shop told me he was able to turn blower motor on - so resistor problem according to him.
On the other hand, I replaced the resistor and it still doesn't work.

So here are the question:
How can I test the blower motor to see if it is really functional (as the technician in the shop indicated) so I can then blame defective new FSU and request replacement. What did he do to be able to turn the blower motor on?

Thanks!
 
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#2 · (Edited)
The FSU connector has five wires in it.
Two are from the battery, two go to the motor and one is a 0 to 8 volt control signal that comes from the HVAC panel.
Jump the power wires to the blower motor wires will make the blower motor spin at full speed.
If you don't know which wires to jump I'll post that info later, not near my schematics at the moment.
You could be missing the control voltage from the HVAC panel.

Jump the Black/Green wire at pin 1 to the Brown wire at pin 4.
Jump the Red/Blue wire at pin 2 to the Red/Green wire at pin 5.
This will power the blower at full speed, the key can be off when you do this.
To test for the control voltage from the HVAC panel connect the + lead of your meter to pin 3, the Blue/Red wire and the - lead to pin 4.
With the HVAC on, manually change the fan speed from min to max, the DC voltage should change from 0-8 VDC.
 
#3 ·
I wrote a detail circuit trouble-shooting below, you can check for pinout diagram etc.

DIY: Trouble-shooting HVAC Blower Motor and FSR
http://www.bimmerfest.com/forums/showthread.php?t=716322

My suggestion:
1. The brand-new FSR might be bad. The quickest way to diagnose this is find another car with known working FSR and do the swap (label which one is which first!).
If this solves the problem, then I guess you can return the FSR for an exchange, BMW warranties their parts for 12m/12K miles I think.

2. May be bad blower motor, but this is unusual.
 
#6 ·
@JimLev and @cn90, first of all, the blower motor is working! Thanks again for your responses and guidance.
I jumped the wires and yes, it started blowing :).
I also checked the voltage and resistance as well as HVAC operating voltage (going from off to max) and everything is OK.

I took FSU out from its slot, with an intention to return it to BMW for replacement, but I decided to attach it one more time to the connector, without it being in the slot but just hanging on the wires (connector). I turn on HVAC and the motor started blowing!
Then, I took my old FSU, attached it to the connector (same way, hanging on the connector and not being in the slot) and the blower motor worked too with the old FSU!?

I return new FSU to the slot and attached the connector - and the blower motor is working.

So, there can be few possible answers for such a behavior:
1. I didn't attach the connector well when I initially replaced the FSU - which I doubt as I attached/detached the connector few times and every time I heard "click" sound.
2. Some of the wires is broken and loses connection when it is in a specific position
3. Both FSUs (new and old one) are defective and they both work from time to time.

I will monitor the behavior for the next few days and update the thread if the blower motor stop working again.

Thanks again for your help!
 
#8 · (Edited)
If all else fails again then you might want to replace the blower motor. It's not that expensive of a part and you could do it yourself to save some cash. Though it is a massive cluster f*** of a job beacuse you literally damn near almost have to remove the entire dashboard to get to it. It's not hard. It just takes a LONG time. Plan for about 10 hours if you did it yourself. Probably somewhat quicker too if a friend will help out.
 
#9 ·
If the blower motor stopped working again it could be a bad FSU or possibly a bad connection where the wires are crimped to the pins.
 
#10 · (Edited)
1+,

Just monitor the blower behavior for now.
As JimLev said:
- Check the connector itself for any bad crimps/wires coming loose (unusual but we have seen this issue before in forum).
My theory is that in the past, some passengers with long legs might have kicked the connector!
- Both old and new FSRs are defective, possible but who knows.

Personally, I'd run each FSR for a full 1-2 weeks. This way you can tell which one is bad.
If both are good, then put the old FSR back in and throw the new FSR in the glove box as a spare.
 
#13 ·
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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