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Does your A/C-heater blower seem like it's possessed? Does it quit working for no apparent reason, then come on again just as mysteriously? Does it run only at one speed no matter what the controls say? Does it keep running even when the car is off and the key is out of the ignition? Your problem is most likely a faulty final stage unit.

Based on what I've seen here and elsewhere, this is a chronic problem with the E39, but fortunately it's a relatively cheap and easy fix. There's a good DIY here, but since questions about it get posted here with regular frequency, I figured it would be a good idea to post one here too. Some of the photos in this post are very large because it's very helpful to see the details if you have no idea what's going on here.

BMW calls this thing the "final stage unit;" the parts guys call it a "blower motor resistor." I'm not sure what the reason for the different terminology is, but it's the same part. The PNs have changed a couple of times over the years, but as of the date of this posting, what you want is PN 64 11 6 923 204 and there's a diagram of the system here. As far as I can tell, the same part is used in all E39 models (but you may want to confirm this). Bavarian Autosport has them for about $70, but they're unfortunately available a lot of places, including the parts counter of your local dealership (I say "unfortunately" because it's a reflection of how often this thing fails).

For some reason, dealer service departments are notorious for not being able to recognize this issue, and may charge you for hundreds or thousands of dollars of unnecessary repairs without solving the problem. If you don't feel confident doing this yourself (i.e., you're the sort of person who is more likely to take an eye out with a screwdriver than a screw), at least bring them this information. Done properly, this is a 15-minute, ~$100 repair.

This is what you're replacing:


(Side view, with highlighter for scale)


(one end view)


(other end view)

The silver part of it is a heat sink. I'm not an electrical engineer, but I believe this thing allows the blower controls to change the speed of the blower by altering the current that passes through it. Inside is a bundle of resistors, and by sending the current through a different combination of leads, it creates the proper current to operate the blower at a desired speed. But resistors generate heat (thus the need for a heat sink), and over time, I suspect the constant heat up-cool down cycle degrades the resistors until they no longer produce the right current, and the controller can no longer send the right signals to the blower. Thus, the blower starts acting strangely despite what the controls are doing.

Now, I've read a lot of horror stories about how difficult this replacement can be, but I didn't find it that way at all. This is an extremely simple operation that took me less than 10 minutes. The hardest part was getting myself into a position where I could get at the faulty FSU.

All you need here is a Phillips screwdriver, a flashlight (the one in your glovebox will work fine) and understanding that you're working with electrical components, not mechanical ones. That means being mindful of how much force you're using. Nothing in this operation requires any great effort, so if you find yourself needing force things, you're doing something wrong.

The FSU is behind the dash in the passenger side footwell. You'll find it easier to work if you pull out the cover under the glovebox. It's not secured by anything, so just yank it out. The FSU is behind a fabric covered plastic panel on the left side:



You want to unscrew the screw (red circle), then slide the panel backward (see arrow), not out. It's also held in place by two metal clips that attach to the frame behind it:



Once you've got the panel out, lay on your back and look up at the space you've just exposed. The FSU is inside there.



Inside the space, you'll see a plug with 5 colored wires coming out of it. The FSU is the thing the plug is connected to, so you've got to get the plug out. The plug is held in place by two clips on the side, and you need to squeeze the clips to free it.



You may find the plug a bit difficult to get out; if so, just wiggle it back and forth until it comes free. Don't yank it out--you may break one of the wires loose, in which case you've just bought yourself an expensive and embarrassing trip to the dealer.

The FSU is itself held in place by another clip at the bottom. You need to push this clip down at the same time you're pulling the FSU out.


(note--plug is still in place in this photo, but take it out first. I didn't take a picture of the FSU with the plug out :rolleyes: )

Again, if you're doing it right, you should not need to force anything. Once free of the clip, the FSU should slide out easily.

You may find all of this easier if you lay on your back in the footwell to get your bearings, then sit up straight, reach under the dash, and do it "by feel."

Now, surprise, surprise, the part you've just removed won't resemble the new one exactly, since as I mentioned, the PNs have changed a couple of times:



Hmm, could this be because the original version was defective? :rolleyes: :dunno: :mad:

Now just slide the new one in the spot the old one came out of. It should slide into place with a "snap" as the clip engages it.



New FSU in place. Note orientation--it will only go in one way. If you're having trouble getting it in, you've probably got it rotated 90 or 180 degrees out of alignment.

Replace the plug, then slide the panel back in the way it came out. Be sure to get both clips into their respective slots, or it will hang loose. Replace the screw.

If you've done everything right, your blower should operate normally now. If it's not, go back in and check the connections. If everything looks right but it still doesn't work, you may have other problems.
 

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Great post. I had to do the same thing a couple of months ago and found it very easy. The only problem I had was getting into position to get a handle on it. I too was surprised at the size difference between the old one and new one. Hopefully these pictures will help someone in the future as it is exactly what they need to do.
 

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Elvis,
Thanks for your help on this!! I paild list for the part at the dealer because I did not want to wait a week. The change took about 20 minutes.
 

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Just replaced the Final Stage Resistor in my 2001 330 yesterday. It's quite a bit more difficult to get to this part in this version car. In my case, after removing the glove box, I had to remove the right footwell air vent. Behind the vent is a stepper motor that also needs to be removed, not too bad here just a linkage and couple screws. There are two screws on the resistor also and they're the same torx fastener as the stepper motor. Not that bad a job, 90 minutes or so. Blower motor no longer possessed!
 

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Thanks for the great post

Holiday weekend...Friday evening 24Deg.C leaving work and my Fan stops working!
Hottest weekend of an Irish Summer and the prospect of no air-con in the car for three days!
I read this post and go to my dealer at 9 next morning and by 9:45 I have my fan back...you saved my bacon...thanks..
 

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Final Stage Unit

Just A Thank You For The Information Relating The Blower Motor Resistor. I Had A Faulty Unit, And Found Your Replacement Info Fantastic,
Many Thanks
Dave
 

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I love you guys. This DIY fix totally saved me so much money. I knew my problem wasn't a busted compressor or controller like the mechanic told me. My friend had the same problem and told me his mechanic just replaced a resistor.

Was kind of a pain getting to the FSR but was well worth the time and trouble. I HAVE COLD AIR NOW!!!
 

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Discussion Starter #12
Man, when I posted this thing, I had no idea it would get this kind of response!

Kind of tells you a few things about how bad this part is. And, still amazed so many mechanics can't recognize it if it's so common.

But--glad to help. :thumbup:
 

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I almost had to pay over $800+ to fix it, but decided to hold off on it and do some research. I think you're right that the first design might have been "defective" or just a "poorer" design since the new one has more bars on the heatsink for greater surface area and cooling.

Did anyone notice any rips or cracks on the shiny / waxy part on the side of the plug?
 

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thanks a million!

I just wanted to chime in and say thanks a lot for posting this. I'm sure it saved me a bunch of money. I just ordered the part for about $70 at bav auto, followed your instructions and pow- it's done. My A/C is no longer possessed!!!

I also wanted to add that before fixing it, this problem actually DRAINED MY BATTERY completely and I had to jump my car to get it running, and it lost ALL of the settings, clock, etc. everything!

That's the only motivation I needed to finally order this part and fix it.

Thanks to you it took me about 20 minutes and it's all done!

I'd also like to add for future reference that I needed a pair of straight pliers to pull the power clip off of the FSU. Used carefully, it works great to push the side clips in while gently rocking and pulling out the power plug.
And the old FSU was very hot when I pulled it out, so be careful you don't drop it on your forehead while doing this repair!

Thanks again!

:) :D :rofl:
 

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BMW Should Be Ashamed

Thank's for the instructions, my wife has a 2003 530i with 54K miles and her blower stopped working entirely. Here's a little story.

The A/C stopped blowing air and I hadn't gotten the BMW manual for it yet so I took it in to the dealership and I figured it would probably just be a simple electrical relay .
They called my wife back telling her ;

1) $440 to fix the blower,
2) The A/C wasn't as cold as it should be and they needed to replace the dryer - $790
3) The plastic components (bushings) of her suspension were cracking and they could fail if she hit a pothole - $825
4) Her fuel filter needed to be replaces - $325
5) They recommended a fuel injector cleaning - $350
6) Her tires were feathering and she needed a 4 wheel alignment - $350

I went online and found your instructions on how to replace the blower relay. It took 15 minutes to replace and cost $100 for the part. Everything works fine and all the other items were BS not to mention 2 to 3 times what they should be charging for the services.

For once crime didn't pay.

Oh yeah I forgot, they charged her $135 to tell her how they were going to rip her off. I ordered the manuals yesterday.
 

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Thank you. Saved me from replacing the climate control unit unnessarily (Had a similar problem on my E36 M3 that was the unit). After reading your description, I replaced the unit in under 15 mins with no fuss or drama. It really was nice knowing the details without having to go "diving" under the dash in 90 degree weather.

Thanks!!!
 

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Fantastic description, just replaced air con resistor in 25 mins, had obviously already been replaced as 2 screws missing.:cry: Now fitted correctly!!!
Many thanks
 

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Thank you for the instructions.
Returned to the airport car park after leaving the car for 2 weeks during a holiday in Spain and the air con was dead.
Did not enjoy the 30 mile journey home on a warm Sunday afternoon with 2 tired and hot kids in the back.
Anyway, arrived home and straight to the internet for solutions to the problem and there it was. There may be criticism of the internet for some of the content available but to find this stuff on line is great.
Managed to pull out the old part in the evening and phoned the BMW dealer first thing. Yes they have the part in stock. Picked the part up from the dealer next morning for £50 and fitted it while in their car park.
Drove back home in air conditioned comfort.
Thanks again and whenever you are in Mansfield, England pop in and I will buy you a beer.
 
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