BMW electrical system pretty good

[fdcg27]

This morning I was driving the old BMW to work when the HVAC blower fan quit suddenly while I was passing through a slice of a small town about fourteen miles from our home.
I hoped that the cause would simply be a fuse and continued on my way. The way home was quite warm since top down is not nearly as much fun at 90F and high humidity as it is at 80F with dry air. AC would have been much nicer but was not an option, since without the fan it would have had little effect.
Got home, changed into shorts and tee and lifted the fuse box lid for the first time ever. BMW divided every circuit and gave it its own fuse. The fuse block of this fairly simple BMW actually has forty six positions, one of which was for the HVAC blower. That fuse was in fact blown so I swapped it out with one of the provided spares and was rewarded with a running blower fan.
Easy.
Nice that BMW isolated the circuits well enough that a single point failure would only take out that function and not a number of others as is more typically the case.

 

[RooflessVW]

I agree! It has been that way for sometime with them. For your amusement, this link shows you my fuse boxes

:

Fuse Box Pinouts

 

[kschachn]

One wonders why it popped though, your blower motor is maybe starting to take too much current.

 

[RooflessVW]

Originally Posted By: kschachn
One wonders why it popped though, your blower motor is maybe starting to take too much current.


If it was the original fuse, they can get brittle over the years. Definitely seen it before, especially the older wire style with the open top.

 

[CharlieBauer]

When they all start blowing, you'll be annoyed for having the expense and time of replacing all the fuses!

 

[fdcg27]

Originally Posted By: kschachn
One wonders why it popped though, your blower motor is maybe starting to take too much current.


In a car that's only twenty one years old?
Seriously, I may remove the blower this weekend and see whether its packed with debris.
This can and does happen over time and would cause a higher than normal draw.

 

[fdcg27]

Originally Posted By: rooflessVW
Originally Posted By: kschachn
One wonders why it popped though, your blower motor is maybe starting to take too much current.


If it was the original fuse, they can get brittle over the years. Definitely seen it before, especially the older wire style with the open top.


+1
I've seen this in older cars time and again.
Fuses do fail for no special reason over time.
If this guy does fail again, that'll tell me that I need to dig a little deeper.
Basically, if it isn't the fuse then it must be either the motor or the switch, most likely the motor.

 

[kschachn]

Originally Posted By: fdcg27
In a car that's only twenty one years old?


I realize it is practically brand new compared to mine, but yes

My motor started squeaking a few years ago and I replaced it then, I tried oiling the bearings but the squeak came back after only a few months. Not an easy thing to replace TBH.

I've never actually had a fuse fail in that car for whatever reason.

 

[fdcg27]

Originally Posted By: CharlieBauer
When they all start blowing, you'll be annoyed for having the expense and time of replacing all the fuses!


Not really.
The time and expense involved would be minimal.
There are really head-scratching electrical problems that the average skilled tech will be no better in diagnosing than you or I.
Those are both expensive and annoying.

 

[MarkM66]

Most blower fans have their own fuse.

 

[meep]

21 year old blower? probably carbon caking around the commutator. I suspect it will blow again, or put a hurting on the resistors or speed controller that drives it. If it's a solid state control, I'd be looking to see how hard the motor swap would be.

 

[supton]

Originally Posted By: kschachn

My motor started squeaking a few years ago and I replaced it then, I tried oiling the bearings but the squeak came back after only a few months. Not an easy thing to replace TBH.


on my Jetta I figured out what to leave off so as to make access to the blower motor easier. It blew a thermal fuse which I repaired, but it liked to squeak. I oiled it once, squeak came back after a few months. Oiled a second time, this made it a year. Oiled it a third (by now I was good at removing this fan!) and it went over a year (and then I sold it).

 

[supton]

Originally Posted By: MarkM66
Most blower fans have their own fuse.

When my thermal fuse went I looked at it, and couldn't find the exact one at Radioshack. I dug around and it turned out that a coffee maker that I was in the process of recycling had the right fuse! Some 4-40 hardware and I was done. [Supposedly if soldered in one must silver solder; I didn't feel like learning how to do that, so mechanical attachment it was. Original was welded in place.]

 

[Silverado12]

Next time you're at a pick-n-pull, grab a handful of fuses. They'll either sell them cheap or give them to you.