# Help - Dometic fridge on 12v



## Jimmad (Jul 15, 2012)

Hi, I wonder if anyone can help with a problem on a Dometic RM 7655L fridge / freezer?

We have recently bought a 2006 Hymer B654, which has this Dometic fridge installed. It was a private sale and when we bought it the previous owner said that the 12v relay behind the fridge was constantly clicking, this didn't sound to be too serious so and we loved the van so bought it regardless thinking we could replace said relay for a fiver and we would be ok! 

However. I am now not so sure it is the relay which is at fault here. I have the manual which includes a circuit diagram and multimeter so had a bit of check. This is what I have found; 

The relay control connections (two thin white wires) are live when the engine isn't running. Therefore closing the relay and delivering 12v and 15amps to the fridge heater connection with the engine not running. 

With the engine running the voltage across the relay control feed drops to 3-4v and of course not enough to trigger the relay and therefore doesn't operate the fridge!

The yellow D+ connection from the alternator works fine and is 0v with the engine off and 14v with the engine running.  

As I had already bought a replacement relay I changed it just in case, however it didn't make any difference. 

So it would seem the circuit is working backwards - ok with the engine off and shuts down with the engine running! Has anyone any experience of this, or advice please? 

Thanks


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## dave docwra (Jul 15, 2012)

Forget the multimeter, get a bulb holder fitted with a 21w bulb & test all connections again, I think you will find a bad connection.

Dave.


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## Deleted member 207 (Jul 16, 2012)

Sounds like a mixed up bit of wiring. Your manual should have the correct wiring diagram - but its always hard to fix up someone else's wiring if they have not followed the colours.

There can also be different methods of wiring - nearly all fridges require 12V to operate the igniter and auto reigniter - some are wired into the leisure battery to make sure that the igniter works. The other circuit is for 12V power to the heater coil which usually is activated only when there is power coming from the alternator. The difference between the two circuits should be easy to spot - the 12V supply to the heater will be heavier wiring than the one to the igniter.

Sometimes 12V problems can be resolved by reseating the spade connectors - over time they build up some crud and insulate themselves. Reseating the connectors can establish the circuit correctly - a squirt of silicon aftwards will fix the problem long term.


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## Jimmad (Jul 16, 2012)

Thanks all for your advice. 

I've checked the wiring against the manual, all looks exactly as it should, correct colours going to the right places etc. just seems odd that the relay is being energised when the engine is not running! There is a feed from the alternator and this behaves as I would expect - 0v when the engine is off then 14v when the engine is running. Just weird that the feed circuit to the relay works backwards! 

 I have also discovered the fridge has not had a safety recall to fix a gas pipe correctly to the back of the fridge, So it's going in to the garage on Thursday. I'll ask them to have a look at the same time, hopefully something simple...


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## cornishlad (Jul 17, 2012)

Jimmad said:


> The relay control connections (two thin white wires) are live when the engine isn't running.



Just in case of a misunderstanding...if both wires are live (at +12v) then this would be the situation where the relay is NOT operated, as seen by test meter readings. 

Of course. whether the fridge is on or of in this condition will depend on whether it is powered via the N/O or N/C contacts.


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## Jimmad (Jul 17, 2012)

cornishlad said:


> Just in case of a misunderstanding...if both wires are live (at +12v) then this would be the situation where the relay is NOT operated, as seen by test meter readings.
> 
> Of course. whether the fridge is on or of in this condition will depend on whether it is powered via the N/O or N/C contacts.



Thanks and yes there is a current flowing accross the relay (one positive one negative) when the engine is off. The relay is a NO type, so I assume this is to ensure that the relay does not draw current when in the off state. Odd that I am getting 3-4v with the engine running, as others have mentioned I am now wondering if a poor connection is somewhere. 

Out of interest does anyone know where the 12v feeds come from on a Hymer B654? I have checked and cleaned the contacts around the fridge, but of course the feed may have a dodgy connection?


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## Brummers (Nov 7, 2012)

Jimmad said:


> Thanks and yes there is a current flowing accross the relay (one positive one negative) when the engine is off. The relay is a NO type, so I assume this is to ensure that the relay does not draw current when in the off state. Odd that I am getting 3-4v with the engine running, as others have mentioned I am now wondering if a poor connection is somewhere.
> 
> Out of interest does anyone know where the 12v feeds come from on a Hymer B654? I have checked and cleaned the contacts around the fridge, but of course the feed may have a dodgy connection?



I have exactly the same problem but mine has worked fine for years it's definitely a component failure of some kind. I also have replaced the relay today which hasn't worked my next investigation will be the panel behind the control knobs. The failure constantly draws current from the vehicle battery which itself is problematic. Have you managed to sort yours out?


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## maingate (Nov 7, 2012)

Hi brummers,

I am sorry that I cannot help you with your problem.

As usual, someone (jimmad) has come on to the forum desperate for help with a problem. Other members help as best they can, only for the lazy tw*t not to follow up and let everyone know what the problem was. If he had, it would have helped you but hey ..... he is alright now so sod everyone else.

There are a number of knowledgeable members on here who are reluctant to offer information because of this.

I hope you can get help soon.


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## n brown (Nov 7, 2012)

quite agree,i've found myself tracking spares,going out to the shed to check voltages or measurements,posting links,and sometimes no response at all-which i suppose means problem solved!a bit of feedback is not just gratifying and encouraging,but lets us know if the suggested solution worked or not. bit thoughtless some folk


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## ian81 (Nov 7, 2012)

Jimmad said:


> Hi, I wonder if anyone can help with a problem on a Dometic RM 7655L fridge / freezer?
> 
> The relay control connections (two thin white wires) are live when the engine isn't running. Therefore closing the relay and delivering 12v and 15amps to the fridge heater connection with the engine not running.
> 
> Thanks



..have you checked the relay earth connection??

...is it a fairly standard automotive relay with 5 blade connectors? If so is the heater wire connected to the correct terminal? (it is SPDT contact arrangement)

I am surprised that the relay is being supplied with 12v when the engine is not running -maybe need to check this 12v feed. Are you sure the leisure battery is charging when the engine is running?


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## churchie (Nov 7, 2012)

This is the wiring diagram link on the internet


Brochure Dometic RM7655L pdf free ebook download from philippe.balladur.free.fr

I have also asked about fridge problems without success. If you google Dometic approved and put in your postcode, it will give the nearest Dometic repair / service centre to you.

Hope this might be of help !


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## churchie (Nov 7, 2012)

Bugger

Just noticed when this was first posted


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## maingate (Nov 7, 2012)

churchie said:


> Bugger
> 
> Just noticed when this was first posted



Yes but brummers has resurrected it as he has the same problem.

Don't be too hard on yourself.


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## Brummers (Nov 7, 2012)

ian81 said:


> ..have you checked the relay earth connection??
> 
> ...is it a fairly standard automotive relay with 5 blade connectors? If so is the heater wire connected to the correct terminal? (it is SPDT contact arrangement)
> 
> I am surprised that the relay is being supplied with 12v when the engine is not running -maybe need to check this 12v feed. Are you sure the leisure battery is charging when the engine is running?



The relay has four terminals a pair for the coil to energise and the 30A in and out connections.  When the engine is running my control panel displays voltage on each battery set and they are both around 14v.
As i said before we have had the van for 18 months and there hasn't been a problem.


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## FULL TIMER (Nov 7, 2012)

don't know if this will help but normally on a four terminal relay they are numbered   85 is earth, 86 should be live with engine running, 30 should come from your vehicle battery and 87 should be the feed to the fridge 12v element


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## mid4did (Oct 20, 2020)

I know this thread is years old but I've had a similar problem so thought I'd put my twopennies worth in,in case someone has a similar fault.
That is the fridge runs fine on 12v/gas and mains withought the engine running but as soon as the engine is running a click is heard and the fridge dies.On a hymer the AES fridge power is controlled from the electroblock and the click is an internal relay switch inside the EBL unit disconnecting the leisure batterys and allowing the fridge to get power from the main vehicle battery.The 12v +ve comes via plug 2 top connector of the 5 port click n lock plug,-ve is port 4,noticeable by the heavier cables.My fault is port 1 is burnt from what looks like a loose connection making and breaking ,although I'm told it could be the fridge 12v heater element faulty.
The unit is now with Apuljack Engineering who are luckily 5 miles away so saving me the cost of posting,£167 + vat to repair and test.Plus supply the new 5 port click and lock for the vehicle.Fingers crossed now for when I put the refurb unit back.
Just down the road from me but I've only just discovered them   
Apuljack Engineering


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