# Dometic RM7655L fridge not working on 12v



## Baron1 (Mar 9, 2011)

Any fridge experts around?
More problems with my fridge! (Dometic RM7655L circa 2005)
I have now discovered that it's not working on 12volts!
On checking the heavy wires to the 12v heating element block I am getting approx 13.5 volts and if I disconnect the plug from the electroblock end it reads 0 volts proving that the wiring from the electroblock to the fridge is ok.
Am I right in assuming that the D+ signal is sent up to the power module and then down to the hab relay when cooling is required?
The habitation relay (new) on the rear of the fridge is not operating when the engine is running.
I have tried connecting a wire from the D+ signal on the 12v connection block to terminal 85 on the hab relay and I can hear the relay operating (with the engine running).
Obviously there is a fault somewhere in the wiring that is not passing the D+ signal to the hab relay, I fear that it’s the power module in the fridge but am open to suggestions…….
I read somewhere on here that someone bypassed the power module as I have done and left it like that and the fridge operated on 12v but with no temp control, is it ok to do that??


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## rayc (Jun 3, 2008)

On my Adria the Elecktroblok sends the element 12v to the fridge on the 'Heating Element' contact block only when the engine is running. This is looped round to the D+ contact of the 'Terminal block DC'. This signal goes to the fridge electronics and gives an output to contact 85 of the fridge relay when the electronics sense it is requires i.e.manual selection or automatic.
It appears from your tests that the relay is not getting the operating voltage on Relay contact 85 so there appears, as you say, a problem with the fridge electronics assuming the D+ signal is getting to it.
As you have found that the relay works when triggered direct from the D+ signal then it could be left like that. Of course the 12v element would always be fed when the engine is running even if the fridge was switched OFF or to gas/electric. This may not be desirable so perhaps you could consider putting a switch into the D+ / relay connection? I was under the impression that there is no temperature control when on 12v but stand to be corrected?
I have photo of my schematic that I used when I had a fault on my RMD8051


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## Baron1 (Mar 9, 2011)

Thanks Rayc,
Your wiring diagram is almost exactly the same as mine! 
I must admit that I was under the impression that fridges had no temp control when running on 12v but I thought that maybe things had changed with more modern fridges.... seems like, and judging by the almost identical diagrams, things haven't progressed much in fridge design!!
I suppose I am asking if there is any risk or danger in my proposed solution and yes I was going to install a switch + light into the circuit.


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## Baron1 (Mar 9, 2011)

Further to my last post, here is my thinking:
If I bypass the Power Module FE103 by linking the D+ directly to terminal 85 of the habitation relay the relay will only be in the operated i.e. closed position when the engine is running.
Once the engine is not running the D+ signal will cease and the AES will after 15-20 minutes turn on to gas operation or 240v if connected to EHU.
So there should be no "conflict of interest" between the different operating systems of the fridge...... unless of course I'm missing something?

Mel.


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## rayc (Jun 3, 2008)

Baron1 said:


> Further to my last post, here is my thinking:
> If I bypass the Power Module FE103 by linking the D+ directly to terminal 85 of the habitation relay the relay will only be in the operated i.e. closed position when the engine is running.
> Once the engine is not running the D+ signal will cease and the AES will after 15-20 minutes turn on to gas operation or 240v if connected to EHU.
> So there should be no "conflict of interest" between the different operating systems of the fridge...... unless of course I'm missing something?
> ...


If you bypass the power module by removing the D+ signal from it would the fridge know that the engine was running or not?


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## Baron1 (Mar 9, 2011)

Rayc, I was going to leave the D+ wire connected to the power module and just put an additional feed in from the D+ connection on the 12v connector block to the relays terminal 85.
This way I think the power module would still be informed that the engine is running. As I said the fridge switches to 12v working when the engine starts but the light on the front of the control panel lights up red not green and the D+ signal is not passed on to the relay from the power module.
As soon as I turn the engine off the AES switches to either gas working (after 15-20 minutes) or 240v working if on EHU.
Hope this all makes sense Ray.
Mel.


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## rayc (Jun 3, 2008)

Baron1 said:


> Rayc, I was going to leave the D+ wire connected to the power module and just put an additional feed in from the D+ connection on the 12v connector block to the relays terminal 85.
> This way I think the power module would still be informed that the engine is running. As I said the fridge switches to 12v working when the engine starts but the light on the front of the control panel lights up red not green and the D+ signal is not passed on to the relay from the power module.
> As soon as I turn the engine off the AES switches to either gas working (after 15-20 minutes) or 240v working if on EHU.
> Hope this all makes sense Ray.
> Mel.


It makes sense but one comment. The element will certainly get power but the indication you have of the red light makes me think that the power module does not see the D+ signal. Therefore the AES would not see the removal of the D+ signal allowing the switch to gas 15 minutes after the engine stops. I do not know what the AES will do if you have gas connected at the same time as the engine running but D+ not sensed by the power module. If it were me I would forget about AES and use manual selection with your modification.


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## Baron1 (Mar 9, 2011)

Ray,
When I have the fridge running on gas and start the engine it switches from gas to 12v so the power module does sense the D+ signal, albeit it does not work on 12v because of the power module not passing the D+ signal to the relay. My reasoning is that if it works that way round it will also work in the opposite direction when I turn the engine off and it definitely works when connected to EHU.
I will double check everything and if there is a problem I will do as you suggest and run the fridge manually.
Many Thanks for your input it's much appreciated.
Mel.


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## WildThingsKev (Dec 29, 2009)

I think the temperature control does work on 12v. I have the same fridge and if I turn the temperature control up or down with the engine running I can observe the leisure battery charging voltage switch between, say, 13.6v and 14.0v as the load from the fridge goes on and off.

Kev


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## Geriatricbackpacker (Aug 21, 2012)

Mel, sorry didn't see this thread as we have only just got back. Are your hab batteries charging when you have the engine running? 
Last year we lost the 12v to the fridge and hab batteries. The circuit was only getting 6v (this is all according to the auto electrician) at the Electrobloc end, the problem was under the dash where the live feed to the Electroblock to tell it that the engine is running and prompt it to trickle charge and run the fridge. The connection was made with a scotchlock and the as the vehicle wire was so thin it had a bad connection. I was able to reconnect it and it's been fine ever since. Sorry it's not in technical jargon but the guy had to dumb down his explanation so I could understand. 
Obviously mine is an older model so they may have come up with a better way of making the connection. Just putting this out there in case it helps.
Good luck...I hate electrical problems.


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