fuse 10 blowing when i turn on heater

[MiniC]

i have a 325i vert im trying to get on the road and i noticed when i started it up the power windows didnt work and the heater didnt changed fused 10 as it was blown and tried again windows still not working and when i tried the heater i heard fuse 10 blow again. rear lights are out and its had a new starter but i feel that is wired correctly. any help would be great cheers!

[Stefan on probation]

Fuse 10

http://www.e30zone.net/e30zonewiki/index.php/Fuse_Box

[Brianmoooore]

Fuse 10 cannot be blown by turning on the heater fan, BUT the heater fan (and mirrors) won't work if fuse 10 is blown. This is because the solenoid coil of unloader relay K7 is supplied with power from fuse 10.
The most common cause of fuse 10 blowing (in fact, the only cause, in my experience) is the rubber covered reverse light switch wires under the car either perishing or getting intimate with the prop. shaft or gear linkage. This applies to cars with a manual gearbox only.
An incorrectly wired, or incorrectly specified, starter motor can also cause the fan and mirrors not to work, along with the windows and heated seats, but in this case fuse 10 would not be blown.

[drakesmith]

reverse light wire causes the no rev counter to work and fuel gauge not to work if irc. Its just a sort. The reverse wire is hitting the body. Change the fuse it ok put in in reverse it will blow.

[MiniC]

Okay I definitely checked. I put it in reverse it was fine. I turn the heater to 3 it pops 100% havnt looked under car yet.

[Brianmoooore]

Do you have the correct relay in position K7?
If a relay were inserted which swaps over the positions of pins 87 and 86, the heater fan would draw its power from fuse 10 instead of fuse 20.

Does the fan work on position 2 without blowing the fuse? If so, pull out fuse 20 and say if the fan continues to run or not.

[MiniC]

im not actually sure the cap is off of k8 which make me feel like someone has been here before and also the fan is not blowing at all on 1 or 2. windows dont work either. i have checked fuse 20 and its fine im quite confused by it all. i had a look at the blower resistors and they seem fine although the connections are rusty each end of the coil.

[Brianmoooore]

K7 should be identical to all of the other orange relays in the fusebox. Pull out K7 and one or two of the others, and check that the pin numbers are identical and in the same places.
K7 is the relay next to fuse 25.

[MiniC]

Alright will try that in the morning. Do you literally pull them out like a fuse?

[Brianmoooore]

All the ones in the fusebox just pull out. The DME and fuel pump relays (on the inner wing) have locating tabs.

[MiniC]

They seem like it. With 85 being closest to the fuses

[MiniC]

Yeh k7 will only go in one way and the pins are the same

[Brianmoooore]

Swap K7 with K2

[MiniC]

Tried it. And it still blew

[Brianmoooore]

Right, it's time to find out exactly where the heater fan is getting it's power from. Since we don't know if the fan motor works or not, I suggest you pull the two wires off of the motor, and connect them to a 12 volt 5W or 21W bulb.
Replace any blown fuses, turn the ignition on, then turn the fan switch on, position by position.
If the bulb lights, pull out fuse 20, and see if it goes out.

[MiniC]

Right I tried that. There is power from the leads and once I remove fuse 20 no power. I assume the motor is knackered. What's your thoughts?

[Brianmoooore]

The motor has most likely seized. A very common problem after 30 odd years without lubrication.
Most can be brought back to life if you spray something like WD40 into the plain bush bearings while rotating the fan by hand and pushing it from side to side. Be careful not to damage the plastic fan blades.
Once it can be spun reasonably freely, take the motor out and power it up in your hand with a 12 volt battery. Spray in more WD40 until it is completely freed up, then let the WD40 dry out, before lubricating the bearings with a light oil, such as "3 in 1", powering it up in your hand again, and adding more oil to the bearings.
Clean up excess oil, especially around the commutator and brushes, and refit, where it'll hopefully be good for another thirty years.
There still remains the fact that there should be absolutely no possibility of the fan motor blowing fuse 10 under any circumstances. The only place that power from fuse 10 comes anywhere near the feed to the fan motor is in and around relay K7.

[MiniC]

Well there was a nest around it this car has been sitting for like 10 years. The bearings are stiff and quite rusty so will give that a go. Do you think it would have anything to do with the power windows not working? Bearing in mind this is a convertible model. BTW thank you so much for all the help on this topic.

[Brianmoooore]

No real connection between your other problems and the windows. The windows are powered, when the ignition is on, through the other unloader relay, K5, and through fuse 17, but now you've established that K7 is working (there's power to the heater fan), then the starter motor connection for the unloader relays must be OK, so K5 should be working as well.
Fuse 10 is not involved in the operation of K5.
Windows should work with either of the doors open and the ignition off, but through fuse 28 instead of 17.
Most window faults are caused by the switches or the push button overload circuit breaker on the front console. Because of the way they are positioned horizontally, they tend to collect contaminants and debris inside of them, tarnishing the contacts. Easily dismantled, and usually repairable.
Keep the buttons facing upwards when you take them apart, if you don't want to be searching for small brass parts and springs on the floor.
Wires have also been known to simply fall off of the circuit breaker. The lucar connectors are far too small for the gauge of wires connected to them.

[MiniC]

im pretty sure now that ive looked in my bentley book that i do not actually have the k5 unloader on my fuseboard so i will need to get one of them. although i though if the heater is blowing ten does that mean its drawing from ten so it will blow at 10 amps as i imagine on setting 3 or 4 its drawing more than 10.

[Brianmoooore]

You've established that the fan supply is through fuse 20 by pulling this fuse out when you had a bulb connected and lit in place of the fan. There's no way the fan should be drawing any current at all through fuse 10.
The higher the switch position the fan is switched to, the greater current it will draw. It will also draw a higher current if it is partly seized, but strangely,if you block the airflow, either in or out, which logically you would think would make it work harder, the current consumption will drop.
The rating of a fuse is the maximum current it will pass without ever blowing, not the current it blows at.
A 10A fuse should pass 10A indefinitely without blowing (although the heat produced would cause deterioration of everything around it). At slightly higher currents it will still take hours to fuse.
I don't know the exact characteristics of blade type car fuses, but as an example, a household 5A plug top fuse will pass 7A for ever, 10A for 100 seconds, about 18A for 1 second, and will blow in about 0.01 seconds at 60A.

[k]

Current consumption will drop as the Fan is doing less work when you block air flow, it's doing less work, passing little or no air when blocked. Less volume flow=less current

[Brianmoooore]

Current consumption will drop as the Fan is doing less work when you block air flow, it's doing less work, passing little or no air when blocked. Less volume flow=less current

Correct, but most people assume the opposite. The revs rise when you block the airflow, illustrating the fan is doing less work.

[MiniC]

Right I have a brand new motor its spins super freely. I put it on as soon as I turn it to 4 it blows fuse ten. Something has to be wired wrong. Right?

[Brianmoooore]

Either wired incorrectly or a wiring fault, such as cables melted together.
Pull out relay K7, identify pin 87 of its base, and feed 12 volts to this pin directly from the battery with a piece of wire.
Does the fan motor work properly now? It should work without the ignition being on.
Check if the reverse lights work without the ignition being on, with the wire still in place.

[MiniC]

Okay I tried that it works fine. Also I plugged in the cigarette lighter and it worked on 4 blew fuse 10 but still worked but it doesn't move on 3,2 or 1

[MiniC]

I also have 2 wires spliced off of the cigarette lighter wires both lead to a 10amp fuse on the wire.