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Awesome (did I see your post somewhere else too?). Thanks! Luckily it was just the FSU this time. :)
 

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First of all, thanks for the excellent DIY, even 5 years later!!
I was a little afraid of tackling this, but all went as planned, until...

As soon as I got the new FSU plugged in (without putting everything else back in place) I put the key in the ignition to see if I now had fan, and nothing. Controls light up, fan appears to be adjustable (according to digital display) but no air at all, just like before. I don't want to reconnect the whole glove box if this part is not what I needed. I'm tempted to put the original part back in (dated March 30 2005) and send the replacement FSU back for a refund.

Any suggestions before I undo everything I just did and start saving up $100s to get the blower replaced? I was scared enough just to take out glove box, not about to remove the head to get to the blower.
 

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If you're not too tight for money I would leave the new FSU in there and just save up for your blower.

FSU longevity is a crap shoot. Sometimes they last forever, sometimes they conk out early. In my case I had the FSU in my 02 conk out in 65k miles. The FSU in my 03 is still going at 126k.
 

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I have also read that the heater valve can cause blower temperature issues.
 

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Just over a year on the replacement from AutoZone and mine is dead.
Got the new one from FCP Euro.
It was quite different in shape.
Fewer tines on the back and the gasket surface did not match the plenum opening.
The sides had some ridges that made it impossible to insert into the opening.
I had to sand it down with the belt sander inverted and I finally got it to fit.

All better now.

Noticed that the old one from Autozone had heat signature all around the one pin onto the circuit board and it was obviously not potted like the new one, just a layer of silicone over the parts on the board.

Here's hoping this is the last time.
 

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Just over a year on the replacement from AutoZone and mine is dead.
Got the new one from FCP Euro.
It was quite different in shape.
Fewer tines on the back and the gasket surface did not match the plenum opening.
The sides had some ridges that made it impossible to insert into the opening.
I had to sand it down with the belt sander inverted and I finally got it to fit.

All better now.

Noticed that the old one from Autozone had heat signature all around the one pin onto the circuit board and it was obviously not potted like the new one, just a layer of silicone over the parts on the board.

Here's hoping this is the last time.
If you dont mind my asking, which brand FSU did you order from us? It sounds unusual that you had to sand it down to make it fit. Just curious if this is something we will need to look into with whats on our shelves.
 

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If you dont mind my asking, which brand FSU did you order from us? It sounds unusual that you had to sand it down to make it fit. Just curious if this is something we will need to look into with whats on our shelves.
In my experience I don't think it's the FSU itself. I saw numerous posts of FSUs not fitting and got concerned when I apparently got one of the FSUs that wouldn't fit (ordered 64116923204, received below).

It turns out the fit was perfect, albeit too perfect, where the insertion angle must be perfectly straight. I found that it was almost impossible to do this if you inserted the FSU with the harness already connected, i.e. the thick gauge wire would c0ck the FSU insertion that the forward ridge of the FSU was getting caught somewhere inside its seat.

I took off the harness and it went in reliably every time.

image
 

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I received the Behr part.

Even perfectly aligned it would not insert to the plenum. The ridges were tapered slightly and the plenum was just too snug since the body of the part was still the same basic size. I only removed about 1/3 the thickness of these ridges (keys?) And it went in tight.

Note that the gasket flange on the New did not match the old, it basically followed the outline of the tines which was triangular in shape. Not like a parallelogram.
 

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In my experience I don't think it's the FSU itself. I saw numerous posts of FSUs not fitting and got concerned when I apparently got one of the FSUs that wouldn't fit (ordered 64116923204, received below).

It turns out the fit was perfect, albeit too perfect, where the insertion angle must be perfectly straight. I found that it was almost impossible to do this if you inserted the FSU with the harness already connected, i.e. the thick gauge wire would c0ck the FSU insertion that the forward ridge of the FSU was getting caught somewhere inside its seat.

I took off the harness and it went in reliably every time.

image
Interesting information. I havent installed an FSU in about 7 years so I can't really remember the experience. Interesting that the precision fit could cause installation issues and it does make sense that it could.
 

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Interesting information. I havent installed an FSU in about 7 years so I can't really remember the experience. Interesting that the precision fit could cause installation issues and it does make sense that it could.
I'm very happy you guys at FCPeuro take a personal interest in our repair projects. Keep up the good work!:thumbup:
 

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I'm very happy you guys at FCPeuro take a personal interest in our repair projects. Keep up the good work!:thumbup:
No problem at all. The more we know about what's happening in the community the better we can serve the community. :thumbup:
 

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FSU DIY job

thanks again forum!
my a/c stopped blowing and i wasn't sure what it was. i did a little research here and once again you guys have saved me headache and cash!!

got my FSU from partsgeek.com for less than $40. the job took about an hour.
 

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2000 323i Touring Auto 130K miles

Finally my original 16 yrs old FSR died. I got new one $50 from BMW Berh Made in China, not Germany. They warranted 1 year so I will see how the Chinese part works.

I removed the two fuses related to AC circuit but didn't remove battery. Removed the glove box without touching those hangers with the rivets.
Removed two T20 screws holding the flapper motor (to gain access to the FSR) and just pushed it away for access to the FSR screws. Trick: placed rag or tissue paper to seal off places that you don't want the T20 screws to fall in. After unthreaded the screw, pull the tool out and then place a magnet on a small screwdriver as a tool to retrieve the screw -- this way it won't fall off into the black hole. For installation, I use the same torx driver (without magnet) with the screw on its tip, carefully on a horizontal line up the screw hole and done. Removed the FSR with its plug, then unplugged the plug the connector. Install: install the FSR without connector, then plug the connector.

People call the thing Final Stage Resistor but the device is not a resistor pot as used in the older BMW. This is a transistor linear power amplifier (as linear audio amplifier with massive heat), or motor driver, takes in an analog control voltage and output a high current analog voltage to control the fan speed, hence it dissipate a lot of heat and so the massive heatsink. Many people believe the very hot FSR was the reason for its failure, and had asked the question why BMW didn't design this motor driver using PWM (low heat loss) instead of linear amplifier? Bmw did use PWM for the radiator and AC fan, so why not for the cabin fan? I believe someone did make a PWM FSR after-maket part before but no longer active. I was interested on this question myself and studied the system during this work. It is fairly easy for me to design a 60A PWM motor driver in the space of the FSR body, and it will run cool like a cucumber. My thought was that due to the sensitive digital control/communication buses in the big wire bundle near FSR location (the FSR's harness was bundled together with many other wires), BMW didn't want to take the change of electromagnet noise generated by the fast switching PWM high current FSR that could cause error in the air-bag system, CAN bus and other buses, and therefore they choose to use the more quiet linear power amplifier FSR. I also think the new updated design FSR is much better compare to the original unit. If one want to use a PWM FSR, one should carefully shield all PWM high current signals from other sensitive wires and buses.
 

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^you dudes are too smart for me... my replacement is still working, but for such a simple job it is a little awkward!
 

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Awesome post - thank you

This was such a helpful post - thank you.
Only thing I ran into was not having the right sized socket or screw for the bolt that holds the white box in place (was one in the very back). I have a peanut-sized carny head and Keebler elf hands though, and it looked like the box was only supposed to come out to provide workable space. So I left it in, worked around it - and voila - heat (reliably).

Was really helpful, thank you.
 
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