Thetford fridge/freezer losing cold on 12v and Gas but not 230v.

[iain26]

A bit of a strange one with our Thetford N3175 3 way fridge/freezer.

Works fine on 230v, if anything it gets a little too cold. Currently my sensors are reading Fridge at 3deg C and Freezer at -14 Deg C.
The issue is when we are travelling and on 12v - the fridge AND freezer warms up too much.
Example, driving 5 hours with a 1 hour stop when it should go onto gas the fridge temp went from 4 to 10c, the freezer went from -16 to -1

Once we stop and the fridge turns onto gas it manages to mostly maintain the temperature but doesn’t reduce it, even overnight, like it does when on EHU.

I have checked the 12v heater and it appears to be working, certainly it is drawing current when the engine is running, you can hear the engine note drop when the fridge cuts in.
I have thought possibly the door seals but again, they look in reasonable condition and why would both doors go at the same time?
I have had fans on the external vents in warm weather which didn’t really do much in the UK in September and now have the winter covers on and again no difference.
I have checked the thermistor is mounted correctly and the fins are “just“ beginning to ice in the fridge and we have been on EHU for a few days now.
I have not removed the fins to replace the paste behind on the assumption that all is well on 230v so unlikely to be this Common part.

I am starting to consider replacing the door seals BUT don’t have confidence that this is the real issue.

Anyone have any similar experiences or any other suggestions to try please.

 

[mitzimad]

Have you tried it without the winter covers we've never found them necessary

 

[iain26]

Yes, ran for a week with no fans and no winter covers and they made no difference.

 

[namwaldog]

Our Dometic RMD8505 had a very similar problem recently and I sorted it out by cleaning the gas flue and burner.....

RMD8505 F/F not cooling on gas - How I fixed it. (inc. pictures)

We have just returned from a week up in Scotland. Not been on EHU at all and F/F was fine up until day 6 when we noticed that the fridge wasn't cool and freezer was defrosting. There were no warnings lights showing and the flue was just warm. When we got home, hooked up ehu, turned off gas...

www.motorhomefun.co.uk

 

[iain26]

The plot thickens.

Fridge set on auto. Running on gas. Start engine, fridge starts clicking between 12v and gas with a clicking noise.
investigation in the power box and it seems the relay in there is clicking on and off, as if it isn’t latching in.
I assume this relay is the one that supplies the 12v to the dc heater when the engine is running.

I have checked the 12v supply is there, both the lc for the control panel supply and the hc for the heater supply And the D+ engine run signal is present. But there is no 12v supply to the heater coming out of the power box.

If I then turn it to manual and select 12v the relay continues clicking but still no 12v to the heater.

My quandary now is to determine if the issue is the Power Control box which includes this relay or the Control PCB which is presumably sending the signal to the relay. Both parts are in the £200 region so I don’t want to order both if I can help it.

Suggestions please!

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[driftwood]

The relay is mechanical and more inclined to fail, if it is clicking over and back its either having problems energizing the coil or the contactor within is failing to fully engage, my money is on the relay
1 other thing to consider, my Dometic used to lose cold when we drove but was fine on gas and EHU. It turned out the charger prioritizes charging the batteries over supplying the fridge so the fridge wasn't getting full power allowing it increase in temp while driving. Then having it too full the gas was only really able to maintain that temp. EHU had the power to bring the temp down again.
I realized one of my batteries was on the way out and constantly calling for charge, when I renewed the batteries problem was solved

 

[GeoffnDee]

Do you have a EM40 or EM50 interface module fitted? (normally behind the driver seat) if so ,it would be worth checking its connections are all ok.

 

[iain26]

Do you have a EM40 or EM50 interface module fitted? (normally behind the driver seat) if so ,it would be worth checking its connections are all ok.

Yep, been there, got the t shirt, on my THIRD EM40 in 3 years. Wrote about it in a separate thread.
I have bnow retired so that the feed for the fridge DC heater comes directly from the engine battery and allows the fridge control unit to switch when it gets the D+ signal (From the EM40)
This means the power bypasses the cr*p connections on the EM40!