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Old 07-31-2021, 06:50 PM   #1
de NO1PC
 
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2004 30' Classic
1988 29' Excella
Campbell , California
Join Date: Jul 2012
Posts: 64
Lost 12vDC to Fantastic Vents, A/C - mystery wire routing

2016 25' Rear Twin Flying Cloud
Intermittent, mostly not working 12v to roof vents, Dometic A/C control. Same (listed) circuit powers bathroom ceiling LEDs OK. (It all worked the last time we prepped and hitched for an outing, did not work when we arrived at camp. Mysteriously decided to work when we got home and unhitched, then stopped working. Does not matter if battery only, on shorepower, with or without solar... that's all well before the DC dist panel.

Yes - 12v good through all fuses at AC/DC distribution panel to all other circuits, lighting, etc. Bummer as this deprives use of any/all ventilation, heating.

Have full detailed schematic diagrams sent from Airstream. Schematic nor other drawings are specific to exact wire routing, junction/splice locations.

According to schematic the same circuit powers the working bath light as the Fantastic vents and Dometic A/C, heater, furnace system.

Using a "fox and hound" wire tracing signal generator and sniffer have traced and verified the wiring to the bath LED (open wire at fuse panel, apply signal to circuit wire, sniff for applied audio signal...)

Uncertain as-yet where the wire to/from the bath light meets the rest of the circuit. I suspect, hope, this may be accessible upon lifting the cover off the A/C unit when I can get on the roof and I'll find a bad splice to fix.

Has anyone had any similar experience identifying such wire routing within a unit, without doing a restore or ripping off panels, etc. ??
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Old 07-31-2021, 07:34 PM   #2
Half a Rivet Short
 
2017 30' Classic
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Carlisle , Pennsylvania
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Hi

Typically these circuits are "daisy chained" together. The master wire hops between the connection points. Connections are made at ( = behind ) the devices involved.

Ground is a bit more random. If your factory paperwork shows you how they run it, great. Often it's unclear. The same daisy chain principle applies ( = connections at the devices ). The randomness comes in when you look at how / where it gets tied to ground. In some cases they do a pretty long ground wire back to a bus bar. In other cases they tag it to a nearby chunk of chassis.

What to do?

Follow the factory drawing as best you can. Find the first device that's dead ( = closest to a working device). Measure it with your multimeter. See if it has 12V to ground. Next see if the ground lead has 12V on it when the device is switched on.

If no 12V on the device, you need to track back on the 12V feed. If you have 12V on the ground wire, you need to follow it back.

This usually involves some guesses and looking at a couple of devices that aren't the ones you are after ....

Bob
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Old 07-31-2021, 08:18 PM   #3
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2007 30' Classic
KW , Ontario
Join Date: May 2012
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Since it is working now I would try to wiggle as much of the accessible wiring in the panel area and hope you find something. Intermittent issues are the hardest to find. And in an Airstream where both sides of the walls have aluminum it's near impossible. The next thing to test is as Bob suggested find the nearest light and remove it and see if there is a wiring issue. You can only hope that you have a loose wire at the connections instead of a wire that has somehow become compromised. I would also just try to remove the light with the issue first. This might take a while but at least you can eliminate those connections.
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Old 08-01-2021, 02:41 PM   #4
de NO1PC
 
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2004 30' Classic
1988 29' Excella
Campbell , California
Join Date: Jul 2012
Posts: 64
Update...

More digging and tracing...

First, it does not work now... so that makes it easier to confirm wire progress tracing from both ends.

Second... found where the harness crosses over to and appears at the curb side toward where all the device wiring seems routed. +12v line tone traces good across that path and to a point of limited access behind a control switch in the wall... and then stops about there - but inaccessible otherwise.

Because wiring from the devices is all behind aluminum skin - no tone trace possible. But so far the gap appears to be in the curb side wall somewhere from 12" above the countertop routing to "in the ceiling" behind the cooktop vent and a cabinet above that. That could mean minimal visible damage if/when it comes to breaching that wall surface.

Meanwhile - I jumpered from the +12v destination connection at the A/C unit to 12v (happen to have PowerPoles in the radio/entertainment cabinet up front) and all of the fans, etc. and A/C unit work "back powered" that way - confirming no shorts, etc.

All that accomplished after 4 hours of messing around... it comes down to deciding when and where to violate the wall/skin at/behind the cooktop vent or the cabinet above and try to dig out the wires and figure out the best fix.

Wife says she's not letting me drill out all the visible rivets and compromising those panels - unless/until we've made arrangements with Vinnie to effect proper cosmetic repairs. For behind the vent unit and the upper cabinet... it's just a matter of time to effect the attempt, etc.

I'm expecting to find a poorly implemented factory butt-splice job that pulled apart... massive time/labor/cosmetic 'cost' for 30-seconds of 'workmanship' issue.
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Old 08-01-2021, 02:54 PM   #5
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2017 19' International
Monrovia , California
Join Date: Jan 2017
Posts: 75
Check the fantastic fan wiring

Since it has not been suggested earlier, Check the wiring on the fan. There are too many connections on this fan making it vulnerable to any loose connection.
You can access the wiring from inside the trailer. I eventually disconnected the rain sensor. Make sure you photograph the connections as you dis-assemble.
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Old 08-02-2021, 08:24 AM   #6
Half a Rivet Short
 
2017 30' Classic
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Hi

A open connection at one end or the other of a wire is *much* more likely than a broken wire. Typically a wire that has an issue against a metal wall or support shorts out before it breaks. Anything is possible, so you may have just "won" the lottery.

If wire nuts are involved, spotting a connection that is open may not be all that easy.

Bob
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