Hi Scott, the
compressor should be OK to use with the new R134a. It is the
oil that is the important part. The
oil is different to the oil used with R12.
The fault in the system could be one of several things. If the
compressor is sealed (totaly electric) then it will be a gas loss due to possibly a leak in a copper tube or plate. If it is
engine driven, it could be the same, but with the added possible of a seal failure around the compressor drive shaft. It doesn't have to be bad enough to see oil leaking, the gas can still escape. This is most common in situations where the unit does not get used regularly.
Another possible is the Drier. Once again due to the
shaft seal, moisture can also get in. It only takes a little over time and enough eventually builds up to overcome the drier and then the Ice will block the system up.
Trying to find a leak is difficult. The first thing someone needs to find out is, does the system have gas. If it doesn't, then the second step is to introduce gas with a special dye. This is because finding a leak is not always simple and a refrigerant gas detector sometimes will not detect the tiny amount leaking. The dye leaves a mark at the leak that is seen with a UV light.
If a major
overhaul is required, then you have to have a new drier installed, new gas, new oil and so on.
It is good to get to learn this stuff. It is probably the most common of breakdowns among a sailign community and the one leaset likely to find a knowledgable person on. Have that knowledge can help with making many friends. And maybe even a replenishment of the cruising kitty. I am still
learning, but have gained a lot of knowledge from just a short time ago when I asked could I put LPG into my AC unit :-0