Originally Posted by Alaskan Sea-Duction
Could just be a bad compressor........
So I ordered another compressor can on eBay for $105.98.
Its a Tecumseh Hermetic Reciprocating AC Compressor AK111JT-004
These units are fitted to pretty much every refrigeration device in the USA and so they are reliable and cheap.
It's quite a job to pull out the Marineair condenser unit and cut out the compressor but is not that hard. There are 3 braze joints to make and the compressor is already filled with oil. Just use wet cloths around the braze area so as not to damage the paint in the area.
Once the new unit was brazed up I did a vacuum check (perfect) and the installed back in the boat. Recharge with gas and "hey presto", perfectly working unit. And very quiet as it is new.
So for half a days work and around $130 its nice to avoid having to spend $2,000 for a new condenser unit when only the compressor is dead.
So thanks to everyone for their help, but this compressor was toast and was never going to be revived. Now it is new again, I am very happy.