AC failure diag help. The saga continues.

[Bdc101]

By the way, anyone know what kind of fuse that is? Would they have it at my local auto parts store? I've honestly never seen this kind of automotive fuse before.

[Clavurion]

Did you measure resistance from that fuse connector against ground so that the wire isn't shorted? Is that fuse labeled 50 or 60 A?

The main fuses Nr.6. Those are "main fuses" and should be available on auto stores.

https://www.realoem.com/bmw/enUS/sho...diagId=61_1338

[Bdc101]

Yep, I checked. With the fan connector unplugged, there is no continuity from the F107 terminal to ground. With the connector plugged in, there is continuity but very high resistance. Not a short. Again, I really think that the bare wire probably shorted at some point.

Thanks, I will head down to my Knecht's later today. Edit: 50A

[upallnight]

Originally Posted by Bdc101

I meant that I measure 12 volts to ground from both sides of the fuse -- confirming that it is not blown or otherwise faulty.



My car is indeed a pre-facelift (production 11/2002). But because it was easy to check, I went and checked fuse F107 anyways and ... DING DING DING!


Fuse F107 has continuity to big red/blue wire at the fan connector -- the one that is supposed to have constant 12v.



I checked fuse F107 and it is bad. There was 12v on the bus side, and 0v on the downstream end. I removed the fuse and I haven't used this kind before; it is not immediately obvious whether it's blown or not. But the DMM says it has very high resistance. So newtis and my Bentley manual are wrong!



I am piecing the puzzle together here. I did find a part of that wire near the connector which had been shaved, probably from getting whacked by the engine bay fan. I realized during this troubleshooting process that that wire has 12 volts all the time, even when the key is out. It must have just brushed the chassis and shorted, and blown the fuse, and since we all thought the fuse was F61 like the manual says, we stopped there. But the wiring diagram was wrong the whole time! I wonder if the other poster (daveking) has the same problem.



My gut was telling me there was no way a #6 wire could have broken without shorting out somewhere, or having an intermittent connection.



Thank you all for your help! And especially wpoll, for finding the wrong wiring diagram that turned out to be right!

The only way that fuse will blow is because the FAN is BAD. It takes a big current to blow a 60amp fuse. Before you do something STUPID like just plug in a new fuse, disconnect the fan connector and plug in the fuse. If it doesn't blow, you know the wiring up to the connector is good. At this point STOP because if you reconnect the fan connector you are just going to blow the fuse again if you are lucky. If you are not lucky you are going to burn out the wires in the harness from the fuse to the fan. If you are real unlucky you are going to have a car fire from the fan short. Maybe that will be a good thing, then you can look for another SUV.

[upallnight]

https://xoutpost.com/bmw-sav-forums/...fan-fault.html

Unfortunately the picture I posted of the post mortem on the fan is no longer available. Thanks Photosbucket.

[daveking]

gona check that after dinner and let you know

[Clavurion]

Originally Posted by upallnight

The only way that fuse will blow is because the FAN is BAD. It takes a big current to blow a 60amp fuse. Before you do something STUPID like just plug in a new fuse, disconnect the fan connector and plug in the fuse. If it doesn't blow, you know the wiring up to the connector is good. At this point STOP because if you reconnect the fan connector you are just going to blow the fuse again if you are lucky. If you are not lucky you are going to burn out the wires in the harness from the fuse to the fan. If you are real unlucky you are going to have a car fire from the fan short. Maybe that will be a good thing, then you can look for another SUV.

Why would the wiring burn before the fuse? The main and first purpose of fuses is to protect the wiring. Wire gauge and fuse amps go hand in hand.

[Bdc101]

Originally Posted by Clavurion

Why would the wiring burn before the fuse? The main and first purpose of fuses is to protect the wiring. Wire gauge and fuse amps go hand in hand.

I was going to say the same thing. That wire (#6 or #8, not sure) will carry 50 amps all day and all night without burning. NEC says a #8 is rated for 50 amps. The fuse is appropriately sized. Like I mentioned above, I found a bare spot on the wire which could certainly have brushed the chassis or gotten wet to short out. I guarantee brushing that big wire against the chassis ground would draw 50 amps.



My car isn't part of the recall in the linked thread (build date 11/2002, but the recall only goes through 2001). I don't doubt that you had that problem, though I can't see the pics.


I will of course be careful working on any 50 amp circuit. I do not want to see a 50A fuse blown on my car or anywhere near me. And I do have a used-but-good fan that I can swap it with if necessary.

[Bdc101]

Additionally, I checked for continuity from the fuse to ground, and there is none with the connector unplugged. With the connector plugged in, there is continuity but high impedance. There will not be a short.

[andrewwynn]

If the insulation is worn off a 50a circuit, it will usually just arc and spark without blowing the fuse. Hopefully you can determine its a defective fan and swap with the spare. You definitely need to address the damaged wire if I read correctly that there was a short.