Yeah Viking,

Good point. The ULT's I mostly work on are revco, which I find good. The sanyo's seem to be more temperamental, however I find charging the 410a as a liquid (as its 50/50 R32 and R125) works ok. You're definitely right regarding moisture/contaminants with these systems. Those complacencies we can get away with (not saying we're complacent but you'll know what I mean) on everyday refrigeration, you can't get away with on these. Everything must be done by the book, ie vacuum measured and recorded after evacuation, charge must be bang on etc. we once had a new low stage compressor on a Sanyo pull down to set point and run perfectly for 48 hours before ceasing. Sanyo wouldn't come to the party as our documentation wasn't up to scratch, even though everything was carried out by the book. I believe it was a failed oil separator which caused the failure and now recommend it is always replaced with compressor. Lesson learnt.
I do enjoy working on these every now and again but give me something over 30hp anyday!