Hi all,
It took a while to solve but this has now been successfully completed.
We had two causes, during the investigations (Paul the Fridge, Haven Refrigeration - based in Ipswich)
changed the thermostat from the new air thermostat to the more common wire around the evaporation plate. In hindsight this created a further complication.
The real culprit was the auxiliary fan. The effect of this was to slow down the internal fan and prevent it doing its job. It was difficult to identify as it was still spinning and appeared to be working. This fault was causing the evaporation plate to clog up with ice.
The solution was to return the air controlled thermostat and disconnect the auxiliary fan. The fridge now works perfectly. I know many people including ourselves use auxiliary fans but for our system they need an independent power source.
Paul the Fridge was excellent. Throughout this he was helpful and reassuring. He followed the problem solving diligently, was always supportive and left us in no doubt that he wouldn't walk away from the job until we were happy. I cannot recommend him highly enough to other East Coast sailors.
Fair winds
Adam