Can you please check what your getting at the AC end, and at least that rules out the inverter?
Reading the manual you need 11.7V of more for the switch on voltage, you have a reading of 11.8V so this should be sufficent all being it very close to the cut off.
Its going to look to pull around 15A at 12V so good chance is the battery voltage will drop bellow 11.7V on startup.
I was initally wondering if the inverter was trying to take DC and pass it through as AC, but it looks like it runs on DC, it also appears its not needing to do anything other than pass through the 12V so there isnt a transformer at fault.
I would say the issue is the battery, if you can pick up another 12V or borrow one from another boat plug that in directly, check the voltage to see if that is above 11.8V and if the fridge starts..
Secondly if that still doesnt start put the two batteries in series and plug it into the fridge and see if that allows the fridge to power up on 24V.
It could be simply your volt meter being 0.2V out, or the tollerance of the fridge not being 11.7V but 11.8V for it to start, and as the battery has aged the voltage has dropped.
The other thing you may notice is that once the fridge cools on mains, the fridge will start working again on the original battery as its not needing to pull as much current on startup.
Let me know how you get on trying with another battery (borrowed or otherwise)
Changing the temp control wont change the current being drawn, as its either ON (drawing ~15A) or on Stanby.
The temp control would just affect how often the fridge starts up to cool it.
My suggestion is set it to 6 when on mains, then set it to 4 when on battery, and you might find for short periods of time it can keep it cool via 12V, but if its set at 6 it means its going to be running for longer to get the temp under control.
Another approach is seeing if the light stops flashing when you set it 1, and starts flashing when you turn it up, as this will certinly indicate if its the voltage dropping when under load (if flashing only once you turn it past 1) or if the battery is completly knackered and not even producing the voltage required under no load.
Good evening Gerry,
I have contacted the Waeco technical department, and their view is that this fault is most likly caused by the battery.
Do you require any further assistance, if not I would appreciate it if you could rate my answer in order for the case to be closed down.
Otherwise reply back and I will happily look to assist you further in anything you need clarified.
Thanks for all your help James,
We're now back from the holidays and managed to keep things cool by switching the fridge on when the motor was running.. it held it when we stopped, so I guess it was the "switch-on current" .ie. we need a new battery.
PS Clicking on rating image does not seem to do anything