Final Stage Resistor fix DIY
 

If you find that your blower motor is pulsing or randomly coming on after your vehicle is turned off, this may be your answer. If your blower motor is on full all the time, this fix may not work as the semiconductors may be shorted at this point. Remove the FSR from your vehicle. Carefully remove the potting material in the corner shown. Go slowly because you don't want to damage the circuit board below. The potting material is soft so this process is relatively easy. You will see two sets of three legs when you have successfully removed this material. To see the board and these pins easier, you may want to put some contact cleaner on the end of a Q-Tip and wipe the board to remove access "small bits" of loose potting material. In most cases, the solder will be broken around these pins connecting to the circuit board causing irratic operation, "blower motor doing it's own thing." Carefully resolder these pins. Make sure you don't bridge any pins with solder. If you do bridge the pins, remove the access solder and try again. Run a small jewelers screw driver between the pins to make sure there are no solder bridges. Once this is done, you are ready to try it. You can see my FSR below. This is what I have done and it now works great. You will see some larger solder connections, I have done this to prevent future problems.
"IF YOU DO THIS PROCESS, YOU ARE DOING IT AT YOUR OWN RISK."
IF YOU DO NOT FEEL CONFIDENT DOING THIS PROCESS, "DON'T DO IT!"

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Good tip, and it should get most of these FSR's back working. The only issue I see is that it can't fix the original cause if the issue which is the inefficient heat sink spikes which let too much heat build up in the unit. The new FSR units are an updated design with more efficient heat sinks to prevent the solder joints from getting heat damaged.

I agree added sink surface would help. Some larger semiconductors would really help, but the issue is the solder pads. These pads are to small. In the original soldering of the unit, all three pads are the same size as the center pad in each set of three. They were nice enough to leave some extra trace (denoted by solder dots) for the outer pins.

Excellent tip. I have an old FSR in my garage I swapped out that I can try this on. Did you reseal it after the repair?

I did not re-seal my FSR. I figure, if anymore problems develop down the road, I won't have to remove the potting compound a second time. I think this is the last time I will have to touch it though. It works like a brand new unit. (has been for some time.)

Cool DIY. Our FSR has been pulsing for a while but it hasn't gone crazy and have the blower motor come on all the time. Also a great chance to brush up on my solder skills!

This has to be one of the best tips I've seen here. Thanks Heising! My fan quit today so I pulled that bastard out, re-flowed the solder joints and its working again.

Not so easy on a RHD car. Pedals are in the way. I've managed to extract the plug from the FSU but cannot see enough to see what is holding the FSU in place. Any clues please or a photograph of the tab etc that must be holding it. By the way the FSU costs about $400 in the UK.

£400 :wow::wow: I'ts an fsr and it costs about £45.Looky here.... Final Stage Resistor : C3BMW Ltd

edit: By chance I came across this thread, I believe every E53 owner should know about this!

Thank you HEISING!!!!:thumbup:

This worked for me and my fan is blowing again...

symptoms: Front vents quit blowing air... everything else seemed to be in order. I could hear the ac trying to work if I hit the "MAX AC" button but no air flow. If I tried turning on the fan, absolutely nothing happened. Rear vents worked BTW.

This is worth a try for anybody that needs to replace the FSR.
I happen to have a soldering iron and have almost no experience with it. (I use it as a wood burning tool) I have never soldered on a circuit-board before.
The hard/tedious part was removing the potting material and not knowing how deep to dig without scratching the green board.
I used a precision flathead screwdriver to remove the bulk and shaved down a popsicle stick to the size of the flathead to safely remove the remainder. Q-tip dipped in alcohol to clean and better expose the pins and circuit board.


It is mentioned in the how-to, but I'll say it again... You don't need to remove the Glove-box to access the FSR. Just the carpeted part where the outlet is attached and the black plastic piece under the glove box where the foot-well light is attached.

Thank you, thank you, thank you!!:D:D:D:D:D:D:D:D