Hi Thomas,

Ice crystals would occur if the filling of the system was not done properly. There is a filter in the system that binds any moisture that may be left at filling time. Normally they replace this filter when refilling. Once a system is working properly there is no interference with the atmosphere so moisture cannot enter. If the system is leaking you may see moisture enter the system after so much gas has escaped that at run-time the low pressure side gets below atmospheric pressure (depending on where the leak is). If you still have the original compressors (you can see this by looking at the way the speed control works). The newer units use a rotary switch if I'm correct. If you still run the originals chances are you have a gas leakage, most probably at the quick-fittings. These are the screw connectors that connect the evaporator to the compressor.
In my case the problem was a leaking heat-exchanger (the tube on top of the compressor) that rotted away due to the salt water in the circuit. In the end I replaced all the compressors.

Regards,

Arno Luijten
SV Luna,
A54-121