Blower Motor Trouble, (not brushes or FSU)

Well, at least I don't think the FSU is the main problem here.

The Car: 96 E36 328is

So I've been having the standard problem of the fan (usually) only running at full speed, I say usually because sometimes I do have control over the fan speed. A long with the fan going away or coming back with a bump at times. Everything I had read pointed towards the fsu, but here is the thing. While investigating, I noticed that a small tap, barely a tap, on the air box would make the motor go on. So assuming it was a poor connection, I ripped everything a part. The connections on the motor seem fine, at first I barely touched the wires where they go into the rubber grommet behind the motor, and it kicked to life. Currently, however, it seems that doesn't do it anymore.

I've tried hammering the motor, to no avail. I accidently made contact between the body and the motor housing...turns out that the motor housing is hot. When that short to ground is held, the motor spins, even with the HVAC system off. Currently the motor seems to run even with the hvac system set to off, though it might just be running slightly longer than usual. ( sometimes it would run a min or two after I shut the hvac controls off ).

Does anyone have any ideas? Is the housing supposed to be hot? This couldn't ALL be from the FSU could it? Doesn't seem like it, especially with the light tap to the air box making the motor spin.

Edit: I've checked and replaced all the fuses, they were all good but I did it anyway.

The housing is not hot. It's lacking a ground. The housing is providing the return path for the voltage. Check for loose/missing brown wires.

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That is what I thought, thank you! I haven't seen any arcing from the motor, so I'll further inspect the connections. I have a suspicion the brn/yellow wire may be frayed, i see electric tape on it.

Are you sure the motor housing isn't supposed to be hot? I kept the wires free from the housing, and it is still electrified. I've bought some contact cleaner and will be cleaning the + and - contacts on it, maybe that will help. But I'm still not sure why the housing is full of power. Is this a known issue for these blower motors?

I am absolutely certain the case isn't supposed to be hot. It's either connected backwards or it has no ground and you are getting arcing to ground when you bump it against a chassis part. If it were connected backwards it would run backwards, and would blow a fuse when you grounded the motor case. Since it hasn't blown a fuse, it tells me your - (minus) side of the motor isn't connected to a ground.

Agreed, which worries me. I'm going to disconnect the battery and clean the connectors on the leads etc, and hope this fixes it. I noticed when I took off the positive and started to put it back on, the motor started to go ever so slightly, and the lead is dirty. From the looks of the design, this motor is completely insulated though, so I'm hoping it's the leads that are at fault at this rate.

A bad fsu wouldn't cause all this would it? I think my FSU could be faulty, but I wouldn't think the other symptoms I've posted would come from the FSU. I'm not sure why it's looking for ground through the motor housing when it's not running. When it is running, it's flowing fine.

Originally Posted by Schuster

A bad fsu wouldn't cause all this would it? I think my FSU could be faulty, but I wouldn't think the other symptoms I've posted would come from the FSU. I'm not sure why it's looking for ground through the motor housing when it's not running. When it is running, it's flowing fine.

There are two carbon brushes inside the motor that make contact with the armature and provide the power to make the motor spin. One of the brushes is connected to the positive terminal and the other is connected to the negative. The brushes make contact with the terminals you connect your wires to via a post the goes through the housing to the outside. If these go through the metal housing on your motor then there is supposed to be an insulator around them to isolate the from the housing. It's possible that one of the insulators has deteriorated and that's why have have an intermittent short.
If you have a multimeter, measure from each terminal to the housing to see if either is shorted to it.

Originally Posted by dc_wright

There are two carbon brushes inside the motor that make contact with the armature and provide the power to make the motor spin. One of the brushes is connected to the positive terminal and the other is connected to the negative. The brushes make contact with the terminals you connect your wires to via a post the goes through the housing to the outside. If these go through the metal housing on your motor then there is supposed to be an insulator around them to isolate the from the housing. It's possible that one of the insulators has deteriorated and that's why have have an intermittent short.
If you have a multimeter, measure from each terminal to the housing to see if either is shorted to it.

Thank you, that is actually my next step...I just have to buy a multi meter. The stores are long enough away that I have to wait until another dry day so I can drive there. I'm thinking I may just have to replace the motor, or perhaps rebuild it...even though it's perfectly good.

I hate electric stuff haha.

I think I may be replacing the FSU as well, maybe that will weed out some problems. When I first pluged the motor back in and turned the electric to the car on, the motor spun up at a constant, but very very slow speed, even though the settings were near max.

Ok, so I replaced the FSU and everything seems to work great now lol. I would like to mention, that the motor IS in fact a ground. That is why it is insulated from the body. Not sure why that information isn't out there...but I'll put it out there lol.