Thetford N3000 series Fridge not cooling on 12v

[Lagos sun]

Help gratefully received.. No points for guessing LOL

Just purchased a 20219 Hymer B MC 690 from a dealer in Germany. Whilst driving 3,000km home (Portugal) we noticed the fridge wasn't working as it should with engine running? Once home I downloaded the Electroblock EBL 30 wiring diagram hoping to check whether there was D+ from alternator to EBL. Unfortunately the downloaded diagram doesn't correspond to how the EBL 30 is wired in Hymer.
I've checked all fuses within double floor of M/H, paying special attention to (2amp & 20amp).. all ok..
The fridge operates perfectly in Auto on 230v and gas.
The fridge doesn't work when Auto or battery operation is selected (whilst engine running)..
The fridge Icons Just flash (green) and the on/off button flashes red.

I removed the outside fridge vent to find there to be a permanent 12v dc supply to the rear of the fridge (thick red & white cables) Whether the engine is running or not, in fact 12v is present when the Hymer 12v control panel switched off ??

My best guess is a relay is stuck.. welded together? Maybe in the EBL 30 unit?
Has anyone had the same scenario/problem on their Thetford fridge?
Obviously too far to return to dealer for repair

 

[Steve N Tracy]

There is a problem with the 12 volt supply 20 amp fuse on the 3000 series Thetford fridges PCB behind the lower vent overheating and failing, there is a superceded PCB from the 4000 series fridges with a upgraded 25 amp fuse and thicker PCB tracks.

 

[pagey]

i have a 3145 in my sunlight twice i have had problems with the 12v the first time it turned out to be the 12v element not to bad to change but you have to move the fridge forward about 1 foot to do this the second time it was the 20 amp fuse that is in the black box attached to the fridge at the bottom, to get at the fuse you need to remove the black box it has the pcb inside it you will find the 20 amp fuse and a 2 amp fuse on the pcb

 

[pagey]

There is a problem with the 12 volt supply 20 amp fuse on the 3000 series Thetford fridges PCB behind the lower vent overheating and failing, there is a superceded PCB from the 4000 series fridges with a upgraded 25 amp fuse and thicker PCB tracks.

hi steve mine now appears to be working according to my multimeter but i was surprised to see the state of melted fuse i took out and also that there was no damage or scorching on the pcb if mine goes again i will source an updated pcb

 

[IRHP]

I had the same problem. https://www.motorhomefun.co.uk/forum/threads/dometic-3-way-fridge-issue.275970/post-5406512