Author Topic: Fuse #20 issues (Read 5441 times)

Eddiedigits · « **on:** August 27, 2012, 06:17:08 AM »

Hey Peeps,

First time posting, so I'll start with a thank you for all the great info which has helped me keep my e30 on the road with my own 2 hands.

I'm trying to get my blower going again, it stopped months ago. AC needs re-gassing but I'm not too concerned about that, it's the heater I want back. Fuse #20 pops as soon as the ignition is turned on. I've unplugged the fan speed switch and the A/C Recirculation switch and the short is still there.

I've opened up the dash and found the point where the power for the circuit splits (green/brown). Continuity tested from this point to each switch and to the connector just inside the firewall. Also tested from that connector to the fuse box. All tested ok, getting a solid beep from the multimeter.

Also tested the diode under the fuse box, as per advice from the forum. The diode only seems to be letting power through one way, but the multimeter doesn't beep. I opened up the little black diode case and it passes a visual inspection.

Any ideas?

Cheers

Ed

EDIT: Also the blower motor is disconnected

Eddiedigits · « **Reply #1 on:** August 27, 2012, 08:23:14 AM »

Started investigating the aux fan even though fuse 19 is fine. But I wasn't sure if it has been coming on at all.

The testing the resistor while still connected wasn't giving me a reading so I tried to remove it and it fell apart in my hand. The ceramic insulation was cracked and one terminal was completely fried the other majorly corroded.

But would this cause fuse 20 to keep popping?

lunchkrispy · « **Reply #2 on:** August 31, 2012, 01:29:00 AM »

When I was having aux fan issues it blew fuse 20 and 19 so I think you may have found your issue.

DesktopDave · « **Reply #3 on:** August 31, 2012, 09:27:14 AM »

That aux fan might have an internal short too, though they're usually pretty reliable - that could cook the speed resistor and pop fuses.

Eddiedigits · « **Reply #4 on:** September 08, 2012, 10:19:46 PM »

Fuse #19 is not popping. With the aux fax disconected, by removing the resistor pack. The problem is still there.
Under the dash, just inside the firewall is a connector for the wiring harness which includes the green/brown power lead for this circuit. With that unplugged the fuse doesn't pop. Plugged in, it does. I read somewhere the fan speed switch can test ok but still have a short so I cut the power wire to the switch.... fuse still pops.

I have started leaving an open bin by the fusebox.

I dont know much about electronics, learning as I go. So don't assume I've checked something obvious.

Cheers

Ed

Eddiedigits · « **Reply #5 on:** September 09, 2012, 10:17:00 AM »

So far I've traced it back past the relays which I think are for the air recirculation. There's 2 relays one has white and one has yellow wires which are connected to 2 identical actuators. One right and one left. I assume this is to switch the air from fresh to recirculation. I've unplugged those and still have the problem. So that leaves the brown wires which leads to something else. I think this has to do with the air conditioning, but the manual leaves me in the dark here. There's no real diagram for the air con wiring and apart from a couple of basic tests it just says to take it a mechanic after that.

I haven't done those basic tests yet as it's almost midnight here and I have to pick my girlfriend up from the Airport soon.

Can anyone shed any light on this?

Also, over the course of trying to find this short I have replaced the tape around the wiring harnesses with cable ties at the junctions to keep it all together. Is there a special tape you should get for wiring harnesses? Electrical tape won't last years will it?

Cheers

Ed

DesktopDave · « **Reply #6 on:** September 09, 2012, 10:43:50 AM »

Those relays are flip flops for the fresh air flaps. They work by having one control pair, one input terminal and two output terminals. The control flips the load from one circuit to the other.

I've taken a few of those apart, but I have to admit I don't understand them either.

As for the tape, I use 'friction tape', fabric tape like OEM. Nice to use as it never shrinks, is moderately resistant to oil, can be torn by hand and best of all only sticks to itself. The only downsides are that the tape won't stretch and the black adhesive does tend to come off on your hands. I've found it for like $4/roll at auto parts shops, HF and (surprisingly) home improvement stores like Lowes.

DanOKC · « **Reply #7 on:** September 11, 2012, 12:43:48 AM »

Sorry, but have to ask the dumb question of, you are using 30A fuse for fuse 20, right ?

If you unplug all of these listed below, so you have 6 loose plugs, does it still pop fuse 20?

blower motor
AC snowflake switch
recirculate air switch
blower speed switch
LH Fresh air relay
RH Fresh air relay

DesktopDave · « **Reply #8 on:** September 11, 2012, 09:00:03 AM »

Quote from: Eddiedigits;115749

Fuse #19 is not popping. With the aux fax disconected, by removing the resistor pack. The problem is still there.
Under the dash, just inside the firewall is a connector for the wiring harness which includes the green/brown power lead for this circuit. With that unplugged the fuse doesn't pop. Plugged in, it does. I read somewhere the fan speed switch can test ok but still have a short so I cut the power wire to the switch.... fuse still pops.

I have started leaving an open bin by the fusebox.

I dont know much about electronics, learning as I go. So don't assume I've checked something obvious.

Cheers

Ed

Pull the three-pin aux fan connector instead to isolate the aux fan from the system. It's a round black connector right behind the valence under the left headlight housing IIRC.

I'm also interested to know if you've unplugged the hot water valve.

You have the ETM, right?

Eddiedigits · « **Reply #9 on:** September 16, 2012, 12:26:43 AM »

Have just finished a marathon effort on the car and found the short... both of them. The recirculation relays which have been replaced have a different pin out to the original Bosch relays. Pins 30 and 86 were swapped so that was grounding the output. Also the wires around the compressor are a train wreck with massive chunks of missing insulation.

With the compressor disconnected I went to work on the relay wiring. Now I thought I had already fixed the pin out issue a few days ago, but my mate was helping me this time and realised I had somehow swapped the pins around in some random configuration that didn't make any sense. Since then I have learned much more about relays and what these one are for. So while he was working on the connectors I took out a pen and paper and figured out the wiring from scratch. They are basically wired up the same but with 87 and 87a swapped so that when the power is cut the polarity reverses and the recirculation flaps close.

We had been at it for a while and were rigging up fuses with copper wire as we were burning through them too fast. I came back with my paper results and had a very different answer to my friend who was just using trial and error. I pointed it out to him and he decided to test his next possibility, as he was about to when I walked in and melted the wiring in seconds.

So after we had replaced all the melted wires (it was only really 2 once we examined the damaged). We wired it up my way and it's all good. Somehow even got all the blower speeds working again, I was only getting high speed but had put off the resistor replacement until I had this sorted.

Now the air con. This has been out of action for a long time so I wasn't sure it would work at all. So we unplugged the pressure cut off switch and the compressor was already disconnected. Bridged the switch wires and tested the compressor power to make sure there would be power if the switch allowed it. Then plugged the switch back in tested again, no power. So the system is too old to turn on without some expert involvement. The wires have been safely isolated and the air con will wait for me to win the lottery.

Also I have reconnected the aux fan (after some testing) without the resistor and upgraded Fuse #3. Just in time for Summer.

While we were in the dash also rewired the stereo, a PO had some very strange wiring in there so we pretty much started from scratch and redid it all which also included hooking up the electric antenna. So now I can listen to the radio and with all the speaker channels and all the speakers working, I can even hear it.

Thank you all for your input. I'm getting some rest then starting on the stuttering wipers....

DesktopDave - I do have an ETM (assuming you mean manual). I did unplug the aux fan and test the hot water sensor after reading your post.

DanOKC - From your list, it was only the recirculation relays. We had wandered off into no-mans land testing electronics as we were at a loss, after reading your post I realised we should go back to the relays and look again.

Cheers

Ed

DesktopDave · « **Reply #10 on:** September 16, 2012, 09:46:38 AM »

Good to hear that you have it sorted. I'm pretty sure I have an HVAC harness off a scrap unit if you need one...I never thought about the wiring being the trouble.

Stuttering wipers are usually dirty contacts in the wiper transmission box. Good luck getting that out - it's a major PITA. I have a spare unit if yours is shot, but usually they clean up just fine.