More on the dead dometic fridge - appears to be wiring problem

GarethHowell

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Further to previous posts on the topic of my dead Dometic fridge; having found a wiring diagram for the 'van I have been able to (maybe) isolate the source of the problem. Unfortunately, it's so strange I need somebody to check my thinking. Here goes.

The Sargent has two 12V wires that go to the fridge:
  1. Thick Red/Yellow from P17. 12V feed to the cooling element - only active when the engine is running.
  2. Thin Brown/Purple from P7. Permanent 12V for the internal light and controls.
I've checked the voltages at the Sargent end and they are fine.

Feed 1 - the switched 12V - is fine at the fridge end.
Feed 2 - the permanent 12V - is only 2V at the fridge end. I've tested the voltage to the chassis and to the two White/Red 0V wires on the connector. I've also tested with the connector made and unmade.

This implies the problem is a fault with the wire. I've never seen something like this before unless the wire is exposed to chaffing. In this case, the wire is in an insulated pair with the other feed. This in turn is in a big loom that runs in a conduit. Also, the fault appeared overnight after we had been on-site for a couple of days.

The next step is to feed 12V from another source to (hopefully) exclude the fridge itself as the problem.

Assuming the fridge is OK, then the dodgy wire has to be the problem. Or am I missing something?
 
Have you checked the fuse on the sargent for the permanent 12V line? It is likely that that wire is not used as standard for anything else so a fuse going could go unnoticed except for the Fridge (it is not unusual to see a noise voltage on a wire that is not connected to a supply.
Given it is in a loom of wires as you describe, it could be crosstalk. I would turn off the hab electrics and check the voltage to see if it drops futher.

Whilst ok for trouble-shooting, using a different source for the 12V permanent feed could be a problem in the long term as the Sargent unit disconnects the habitation electrics as soon as the engine starts (or you turn off the electrics from the panel also). This means that when you start the engine, the fridge will not work on any source as it has no 12V to the electronics of the fridge and so goes off.
 
Thanks for that. I don't think it can be a fuse because there is 12V at the Sargent end of the wire. I did check fuses - pulled them and re-wiped them - but no change. I will check again though.
I take your point about cross-talk. That would explain the 2V.
 
I had a look at your other post with a link to a 2014 Schematic for a Sargent 4xx Distribution Unit. I know you said it was just the nearest you could find rather than maybe exactly what you have, but given that is the best current view available, so we assume a reasonable starting point ....
The Fridge Permanent 12V comes from the wire on connector P7. It would seem to also be the only wire coming out of P7 as well. Could it be as simple as P7 having a loose plug?
On the same set of Schematics, there is another 12V permanent on Connector P3 (same colour - Sargent always use that Brown/Purple for permanent 12V). If that is live but the P7 Brown/Purple is not (possible internal break?), maybe join the P7 wire and the P3 wire together and hopefully get you the permanent 12V fridge feed (assuming no wire break in the line).

It does sound like you have a wire fault though from your check :( Could you repurpose one of the other wires in the loom to be a permanent 12V and splice that wire into the permanent at the sargent end? Running another wire end to end could be a real nightmare (though not impossible - I went along one side, underneath, across and up the other to run a temp sensor to the fridge, and that could have been a 12V line just as easily).
 
I'll spend some time tomorrow on this. I'll report back.
 
OK, I think I’ve confirmed it’s a wiring problem. I connected a 12V battery direct to the fridge and everything works. That excludes the fridge - leaving only the loom as the source of the problem.

As a temporary fix, I’ll just find a way to feed a separate wire through from the control box. Damned annoying though.
 
GarethHowell said:
OK, I think I’ve confirmed it’s a wiring problem. I connected a 12V battery direct to the fridge and everything works. That excludes the fridge - leaving only the loom as the source of the problem.

As a temporary fix, I’ll just find a way to feed a separate wire through from the control box. Damned annoying though.
Click to expand...
If you are able to feed it, I would suggest maybe using some multi-core cable (if one wire has chafed through, other ones in the same loom may be on the way out? Could be worthwhile having the spare lines ready).
 
wildebus said:
If you are able to feed it, I would suggest maybe using some multi-core cable (if one wire has chafed through, other ones in the same loom may be on the way out? Could be worthwhile having the spare lines ready).
Click to expand...
It’s tempting, but I have no idea where the loom is routed As it’s behind stuff all the way. All that appears in the fridge compartment are the four wires required for the fridge. Short of ripping out the toilet/shower cabinet, I can’t see further.

I’ve found a route forwards from the fridge compartment into the leisure battery box, through the other side of the battery box at low level, along the floor as far as the bed box and then into the bed box to reach the controller. I can hot glue the wire into the corner and then run a bead of silicon over it to hide it from view.

I thought of just connecting direct to the leisure battery via a fuse. It would stop the fridge being shut down using the “system shutdown” button on the controller, but might also have other side effects if something else is fed from the that wire.
 
Generally (and originally) it was used for the Fridge Electronics and Dash Radio (if it was rerouted from the Starter Battery supply), but things have developed as motorhome and caravans have got more complex and fancy and the EC4xx setup you have is Sargents fancier one for sure.

Out of interest, does the "system shutdown" actually shut down EVERYTHING? On the other Sargent Units, the Control Panel "OFF" button does the same as when the engine starts and the EMC relay kicks in ... Everything is turned off EXCEPT the permanent 12V supply. But they don't have things like the heating controls as part of the control panel but are kept separate.
 
wildebus said:
Out of interest, does the "system shutdown" actually shut down EVERYTHING? On the other Sargent Units, the Control Panel "OFF" button does the same as when the engine starts and the EMC relay kicks in ... Everything is turned off EXCEPT the permanent 12V supply. But they don't have things like the heating controls as part of the control panel but are kept separate.
Click to expand...
I’ve just been out and tested. As far as I can tell, it isolates everything 12V that wasn’t part of the original van - control panel and associated equipment, fridge, and aerial amp. The only item I can’t test is the step; because that also is busted.
 
Hannah the c5 nut said:
If you get stuck I can help, where are you located? I am a motorhome electrician
Click to expand...
Thanks for the offer. I've done it now.
I drilled through from the fridge space into the leisure battery box and thence to the walkway. Then I ran a wire back to the bed box and to the controller. I simply connected it to the existing wires using those insulation-displacement connectors. Spot glued the wire in place with hot glue and then ran a bead of solicone over the hole lot to protect it.
All working now. Next job is the step!
 
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GarethHowell said:
Thanks for the offer. I've done it now.
I drilled through from the fridge space into the leisure battery box and thence to the walkway. Then I ran a wire back to the bed box and to the controller. I simply connected it to the existing wires using those insulation-displacement connectors. Spot glued the wire in place with hot glue and then ran a bead of solicone over the hole lot to protect it.
All working now. Next job is the step!
Click to expand...
What's up with the step? just curious really as I need to fix my step as well and we probably have exactly the same step fitted! mine comes out partly by itself; and if I help it goes the full distance, so thinking the gears are maybe full of muck? putting off looking at it due to cold weather (that is what I am telling myself for the last 6 months anyway :( )
 
GarethHowell said:
Thanks for the offer. I've done it now.
I drilled through from the fridge space into the leisure battery box and thence to the walkway. Then I ran a wire back to the bed box and to the controller. I simply connected it to the existing wires using those insulation-displacement connectors. Spot glued the wire in place with hot glue and then ran a bead of solicone over the hole lot to protect it.
All working now. Next job is the step!
Click to expand...
Just a quick question ..... "insulation-displacement connectors" ... is that a fancy name for the blue "scotch-locks"?
If so, I really would suggest a better connection. They age very badly over time and give intermittant problems (they get used a lot for Towbar electrics and are a bit of a job-creation scheme with the amount of rework needed)
 
Our step used to ‘stick’ and then would come all the way out with a helping hand.

I found blasting it top and bottom with a pressure hose to get rid of all the road dirt and grit etc, then a liberal spray with a silicone lubricant did the trick.

Best avoid spraying the top of the step, as you don’t want it slippy.

Paul
 
paulhelenwilko said:
Our step used to ‘stick’ and then would come all the way out with a helping hand.

I found blasting it top and bottom with a pressure hose to get rid of all the road dirt and grit etc, then a liberal spray with a silicone lubricant did the trick.

Best avoid spraying the top of the step, as you don’t want it slippy.

Paul
Click to expand...
was that with the side cover removed, for example? or just as it is still all intact?

I looked around mine (not disassembled in any way) and it looks remarkeably clean - but it still acts just as you describe yours did.
 
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