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Discussion Starter · #1 ·
I apologize in advance if someone has already made a thread about this, but I could not find anything that would fix my issue.

A while ago in the summer, my fans were only blowing heat, and I could not change the speed of the fans, turn them off, or change the temperature.
Eventually, the screen on the climate control unit shut off, but the buttons were still lighting up. The fans started running for 15 minutes after any door on the car was opened. A few days later, the fans would run until my battery is dead. I read up some forums, and it seemed like the FSU was the problem. So I ordered a new one, and kept the old one unplugged until the new FSU arrived.

When the FSU arrived, I installed it, but the fans just kicked right on, and started blowing without the car being on. I unplugged it, and tried something else.
I read that it could be the ambient temperature sensor under the front bumper of the car. I replaced that, plugged in the FSU, no luck. The fans did the same as before, and no display on the climate control unit.

I visually checked all the fuses in the glove box and trunk. None were bad (visually).

I went as far as replacing the climate control unit, no luck.
BUT THIS TIME when I plugged in the FSU after replacing the climate control unit, the fans did not turn on at all. I still do not get a display on the climate control unit, but the buttons light up.

I have absolutely no idea what to do now, and the nearest shop that works on BMW's is hours away. I need this car for work. If anyone has any ideas, I would appreciate it more than you could imagine. I still have heated seats and heated steering wheel, but its still chilly here in Pennsylvania :)
 

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What year and model? Mileage?

It does sound a little like a climate control module. Is the replacement module known good? Where did you get it? Also, I read that there are some compatibility issues with used climate control modules, and that you might not be able to use a later e39 (post '00) climate control module with an earlier car and vice-versa (not sure on this). Check #'s on RealOEM.

Is the replacement FSU new ?

It also sounds a little like the fuse box (aka junction box) under the front passenger carpet is acting up. This is an area that can attract water, corrode and cause a whole host of problems. you can check it by removing all 4 bolts to passenger seat, unplugging seat electrical (unplug battery first), tilt seat back and pull up carpet and open junction box cover.
 

· Wingnut
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^^^ what he said.
just as an FYI, replacing the outside temp sensor wont affect the issue youre having. if it croaks, youll read either -40 (open thermistor) or +120 (shorted thermistor) on the cluster, heater mirror will stay on if you have them and can discolor the mirrors and A/C is inhibited on some E39 models with a -40 reading.
visual fuse check isnt reliable, fuses have been known to crack and become intermittent/open. probe the applicable ones.
 

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Discussion Starter · #4 ·
What year and model? Mileage?

It does sound a little like a climate control module. Is the replacement module known good? Where did you get it? Also, I read that there are some compatibility issues with used climate control modules, and that you might not be able to use a later e39 (post '00) climate control module with an earlier car and vice-versa (not sure on this). Check #'s on RealOEM.

Is the replacement FSU new ?

It also sounds a little like the fuse box (aka junction box) under the front passenger carpet is acting up. This is an area that can attract water, corrode and cause a whole host of problems. you can check it by removing all 4 bolts to passenger seat, unplugging seat electrical (unplug battery first), tilt seat back and pull up carpet and open junction box cover.
I have a 2002 530i
The replacement is known good, and it's from a year similar to mine. I bought the FSU new from FCP Euro.
I'm checking the fuse box under the carpet now, there does not seem to be any water.
 
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