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Old 02-04-2013, 07:21 PM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
Join Date: Mar 2008
Posts: 19,181
Mein Auto: 02 BMW 525i M54 automatic
It could be, as you suggest - as I don't know WHAT the problem is just yet - but - I know what to do (which is my homework).

O'Reillys said the battery & alternator were OK. Here's a picture of the O'Reillys tool in action today ...

Then I took it to Autozone, where the battery & alternator tested good a second time (showing 14.13 volts at idle):

So, now it's time to check the FSU out, even though it was replaced in 2009 (I haven't noticed any blower fan problems ... but that's the next thing I'll do).

Doing my homework, I find these quotes scattered about the forum, which relate to unplugging the FSU fuses:

Originally Posted by pleiades View Post
That's a single, square socket housing for two large fuses, F75 & F76, unlike the individual socket arrangements shown in the attached photos. And yeah .... it's hard to get your hand up in there (be sure to disconnect the battery first), let alone finagle the fuses upward and out with your fingers. Be sure to put the right fuse back into the right slot, too. Easily interchangeable.....
BEHIND GLOVEBOX (look from underneath):
F75 = 50A, Auxiliary fan (some say it's red)
F76 = 40A, Heater blower (some say it's yellow) [cn90 says it should have 12V when HVAC is turned on]
Originally Posted by JimLev View Post
Pull the bottom plastic panel off that is under the glove box, pull it straight back toward the seat.
Then unhook the side supports for the glove box.
This is what your will see.

Originally Posted by rog5878 View Post
To access F75 and F76 ... close the glove box and behind the glove box is a plastic panel with a hole in it (the panel is directly behind the glove box) Pull it towards you. Takes a bit of a nudge.
Then there are all kinds of wires bound together and various connectors that if you pull out will probably incapacitate the car -- who knows. I had to contort myself to lay on my back and look up in the well on the passenger side.
Yes, the two large fuses -- 75 and 76 are in the middle of this mess, and yes, it is a tight fit (took forever to locate them with the little flash light; some say they are obvious but they weren't to me; of course, now I know exactly where to look). God knows how one gets them in. To get the fuses out, I had to nudge the first fuse on each side -- couple of sparks -- God knows what those shorts did -- and finally it came out -- the fan stopped.
Originally Posted by bluebee View Post
1. Car dies periodically (and blower has wierdities at the same time)
2. Unplug FSU ...
3. If intermittent battery death stops, then you've pinpointed the problem
4. Replace FSU
If it's not the FSU, then I'll need to go, one by one, down all 88 fuse slots (F1 to F114).
To measure the current drain from your battery you will need to connect your multi meter in series with the battery ... To measure current disconnect the negative terminal (I use the neg but you can use either), set your millimeter to measure amps and connect the meter between the battery terminal and the disconnected cable. If you don't have an amp meter then use a 12V test light bulb. The bulb will have a very low glow due to the current drawl from your clock, computer, etc. If the trunk light is on you will want to pull the bulb or fuse. If it is brighter then a low glow then you have a short somewhere in your car. If you want to see what the difference between a low glow (low amp draw) and a high amp draw turn on your head lights. You can pull each fuse and see if there is a change at the amp meter or pull the fuse and insert the amp meter across the fuse terminals (need to reconnect the battery of course). Checking each fuse (by pulling or direct measurement) will tell most problems except if you have a worn wire short on the hot side (positive) of the fuse box which is very unlikely.
Originally Posted by bluebee View Post

Here is what I think each pin does:
#1 = ground
#2 = 12V power, 40 amp fused
#3 = input to fsu from heat/ac module
#4 = output power to the blower motor? (speed 1?)
#5 = output power to the blower motor (speed 2?)

And, here is what I measured between each pin and ground (the FSU body):
#1: Old FSU = 600Kohms, new FSU = 11.2 ohms
#2: Old FSU = 3.02Mohms, new FSU = 1.22Mohms
#3: Old FSU = 2.22Mohms, new FSU = 608Kohms
#4: Old FSU = 2.14Mohms, new FSU = 602Kohms
#5: Old FSU = 3.05Mohms, new FSU = 1.28Mohms
NOTE: For the wiring diagram below:
F76 - Fuse 76 (yellow, 40 amps, under glovebox and above GM3 connector X254).
15 - Ignition power (RUN & START)
30 - Batt positive (+)
31 - Batt negative/gnd (-)

Originally Posted by rjjarvis View Post
Elvis, this is a fantastic writeup and saved me money and grief. I have a couple of comments:

1. BLOWER STOPS WORKING COMPLETELY. This repair also works in at least some cases when the blower STOPS WORKING ALTOGETHER. A lot of the web-based commentary seems to imply that the FSU replacement only fixes blowers that are intermittent, or that have speed problems. In my case, the blower stopped working at EVERY SPEED. It was just like it was switched off. I followed all the commentary and tested it at all speeds -- NOTHING!! I was really afraid then, that the blower motor was kaput, and not the FSU, based on all the comments. But I decided to try the FSU first, and I'm glad I did. For $52 bucks, free shipping from autohausaz, it was really worth a try.

2. CONTORTION. For me to do this repair, I had to lower the passenger seat down as low as it would go, and move it as far back as possible, into an almost bed-like position. Then I climbed into the seat backwards, with my feet toward the back of the car, my body upside down, so I could get my head and arms underneath the dash, facing up towards the FSU. It's very close in there, but even a monstrously large person like myself (6'2", 280 lbs) managed to get in there with some difficulty. If you have a small, thin person in your family who is very flexible, you may want to engage them for the removal and installation of the FSU.

3. FUSES. Of course, the first thought is to check the fuses. Once the "easy" ones in the glovebox are checked and found to be ok, the thought is that Fuse 75 or 76 might be to blame. They are big 50 amp fuses that are located in a very difficult place, behind the glovebox. I know there is a lot of commentary out there about how to remove them. But REPLACING them is something else altogether. No one mentions that there is an aluminum brace that is in the way. After diddling around for a long time, I found that the only way to REPLACE those fuses is to jam your hand in back of the aluminum brace by force, and punch the fuses in from the top. The aluminum brace will move enough to let you get your big fat hand back in there if you use force. Of course, in my case, all of this was wasted, since the fuse was not the problem. However, to get to the FSU, it really helps to have the glovebox out of the way anyway, so all the effort was not wasted.

4. FSU REPLACEMENT. Make a mental note of the orientation of the FSU as you take it out. There is little space to work down there, and it is very difficult to keep turning the new one around trying to fit it back in. Plus the new one is not exactly the same shape as the old one. I printed out a picture of the FSU in place from Elvis' DIY and brought it with me out to the car. That really helped. Nevertheless, be prepared for some jockeying to get the old FSU out, and the new FSU in -- the only thing that I was concerned about was damaging the very soft prongs in the new one while installing. Luckily that turned out to be not a problem.

5. SOFT PRONGS. I should note that the new part, from BEHR (the old one was made by VALEO) had very soft prongs. The old one's prongs were very hard and could not be bent, but the new ones were very bendable. In fact, I thnk I accidentally bent them a little while fooling with it. I did not know whether this made a difference, but where they touched each other, I bent them back so that they did not touch, and were aligned in neat rows. Maybe this made no difference, but I didn't want to take the chance.

In my case, as soon as I replaced the FSU, everything went back to normal! It's like magic. I was dreading having to disassemble half the car and replace the blower motor -- but that won't be necessary, thanks to our friend Elvis! Really appreciate what you have done here for all of us.

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Last edited by bluebee; 02-13-2013 at 04:27 PM.
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