Date: Thu, 22 Jul 2010 23:35:08 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: A/C Wiring/electrical help (pic)
In-Reply-To: <016101cb2a09$25caefc0$7160cf40$@com>
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At 09:48 PM 7/22/2010 Thursday, Robert Fisher wrote:
>http://picasaweb.google.com/garciasghostvw/ACWiring#
><http://picasaweb.google.com/garciasghostvw/ACWiring>
That's a classic example of a high-resistance connection on the end
that melted. You can see that the link itself hasn't even had to
breathe hard. However I would expect given the photo that it would
still work in this condition, just that the far end would continue to
get hot until the poor connection was found and fixed. Notice that
the sleeve on the crimp fitting isn't melted, so that pretty much
limits it to the actual connection between screw and terminal and the
link itself.
>Given the condition of the link I was thinking I might replace it with
>something like this:
>
>
>
>http://www.tti-plus.com/8-Gauge-MAXI-Fuse-Holder-W-Weather-Cap-50-AMP-Fuse-p
>/tti-maxi-f8g-50.htm
I can't see any reason not, with the caveat that all these
high-current circuits need pristine connections or localized heating
will cause damage. That includes the connection between fuse and
socket -- that's perhaps why the existing link is bolted on instead
of plugged in. I have had an 80-amp ATC-type fuse (in-line in an
inverter supply circuit) melt one side of the socket (like the one
you pointed to but perhaps larger) and seriously distort the plastic
of the fuse itself, exactly as your link did and for the same reason.
>The thing is that I don't know if something like that is appropriate
>compared to the characteristics of the fusible like (slow-blow or fast-blow
>or whatever). I don't want to put the wrong thing in there.
I think it's fair to say that automotive fuses in general are
slow-blow. That doesn't necessarily include the small glass fuses
for low-draw electronics. A fifty-amp ATC fuse is not going to be a fast-blow.
>Secondly, does anybody know of a systematic approach to troubleshooting the
>A/C electrical system?
Robert, I haven't studied the A/C circuitry (since I don't have one)
and I don't plan to do it tonight, although I'm willing to work
through it with you when you run into problems. I definitely would
suggest that you copy the schematic, get some colored pencils and
read my wiki article on figuring out schematics. Holler when you get stumped.
> It has a ton of relays, for one thing, and I'm not
>sure how one would test those.
You test them by pulling them out, energizing and de-energizing the
86/85 terminals and checking for correct continuity on the other
terminals as shown on the schematic. If it's a simple four-terminal
relay then you should have continuity between 30 and 87 when the
relay is energized, and not otherwise. You should be able to hear
the click as the relay pulls in. The continuity buzzer on many
multimeters is not sufficient; a better way is with battery and a
stoplight bulb that will actually pull some current through the relay
contacts. But at minimum you need to see zero or at absolute most
maybe a tenth of an ohm with a meter. Seriously, rig up the
stoplight bulb, that will draw a couple amps or so and prove that the
contacts will actually pass current. Measure the voltage drop across
the contacts while the bulb is lit -- the closer to zero the
better. A hundred millivolts with that load I'd consider marginal at best.
> I'm hoping to avoid the brute-force approach
>of following the current from the fuse block back to the compressor and fan,
>etc. while the engine is idling or the system is jumpered live or
>what-have-you.
With the caveat that you'll be following the voltage and not the
current, I'd suggest that doing exactly that is not at all
brute-force but (in combination with the schematic) the proper and
intelligent way to troubleshoot any Vanagon electrical
fault. Replacing stuff at random is called "shotgunning" and is
otherwise known as the expensive way to (maybe) fix a problem -- not
as bad as running at the coal fyce with yer 'ead, but more in line
with scrabbling at it wi' yer bare 'ands. I say (maybe) because
often the problem is in the wiring.
>Help? : /
Is that at least a crumb?
Yours,
David
