# Dometic RM7405L AES Fridge - not auto selecting 12V



## dwwwuk (Dec 31, 2005)

Don't know if anyone else has experienced this problem - I have a Dometic RM7405L Fridge in my Bessacarr Motorhome and it works fine when not using the 'Auto' function - i.e. I can manually select Gas, Electricity and 12V - the LED on 12V goes from red to green when I start the engine.

However, when on Auto, it just tries to light the gas and I believe it should switch to 12V?

I was quoted £185 + VAT to fix it when in for a service, too much given I can manually switch it - but it anyone knows either what the fault is and how to fix it or alternatively how easy it is to remove the fridge so I can check out the PCB that would be appreciated...

Best Regards,

David


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## wilse (Aug 10, 2007)

I think 12v only works when you are driving! Hence the LED going from red to green.

Also after driving, when you stop it's normal for it to takes 10 mins etc to switch to gas [if left on auto].

w


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## dwwwuk (Dec 31, 2005)

wilse said:


> I think 12v only works when you are driving! Hence the LED going from red to green.
> 
> Also after driving, when you stop it's normal for it to takes 10 mins etc to switch to gas [if left on auto].
> 
> w


Hello, thank for the response - it's kind of the opposite, it just keeps on trying to light the gas!

It's only switching to 12V if it's manually selected as 12V, it's as if AES isn't registering that 12V should be on when the engine is running.


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## wilse (Aug 10, 2007)

Does the fridge work if you manually select 12v and have the engine running?

IF so when the engine is running and it is automatically selecting gas [when in AES mode], then my guess 8O is either a fuse, or relay/connection.

I've had similar, it was a fuse.

I have a little blue relay that I think senses when the engine is running and directs power to the fridge.

Hope it's not an issue in your fridge!


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## DaveJM (Dec 29, 2008)

David,

I have a Dometic RM 6505. The PCB is behind the control panel and is easy to get at. I didn't need to remove the fridge. When I had a similar fault I sent the PCB to Dometic who tested it and it was faulty. I bought a new one for £200 because I didn't have the manual option. I found Dometic very helpful.


Regards


David


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## dwwwuk (Dec 31, 2005)

wilse said:


> Does the fridge work if you manually select 12v and have the engine running?
> 
> IF so when the engine is running and it is automatically selecting gas [when in AES mode], then my guess 8O is either a fuse, or relay/connection.
> 
> ...


Hello, yes, the fridge runs fine if I select '12V' manually - light goes green and it chills fine.

Just on AES it's not recognising 12V - I noted that if you manually switch to 12V with the engine not running, you get the LED on 12V illuminated but red, when you start the engine it turns green and cools (which is the normal behaviour I believe for 12V option.)

Makes me think that it may not be a fuse as the fridge seems to be '12V aware' based on the 12V setting. When it was discovered (pardon the pun!) while in for service (at Discover) - they suggested it needed a new PCB for the fridge


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## tramp (May 25, 2005)

Hi dwwuk..

our Burstner does the same thing and has done since a new [they said] pcb board was fitted at change over to us by Highbridge...

A dometic agent near to me who I trust tested the circuit and could find nothing wrong.. the power was getting to everything IT SHOULD..but try this..

when van on mains select atuo and it goes to mains -yes- NOW press the heater bar switch and ours bleaps saying mains connected..dont know id beesys have this function, it dont do it if mains not connected.

We have for the past 18mnths fulltiming used the van manually when not on hook up with no probs and when on mains use the auto incase the mains trips then it goes over to gas...

hope this helps..you aint alone out there :lol: :lol:

To me and I aint no electric bod..there is a fault in the board auto select sequence..but I aint paying £200 just to prove me wrong when it works fine otherwise..


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## Jean-Luc (Jul 21, 2005)

I had this problem, it may help.
Fridge wasn't 'seeing' 12v and going for gas when engine running, sometimes.

Turned out the voltage regulation on my alternator was 'gone off' a bit and when a heavy load cut in eg. AirCon fans or B2B, the voltage was dropping to about 12.8 ish which was too low for the fridge so it went looking for gas when on 'auto'.
I recon if I didn't have AirCon the problem wouldn't have showed as 'normal' loads were being handled OK

Replaced alternator and all now OK.


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