I hate to think there is scheduled maintenance on the compressor. Sometimes it's better not to know! I have the manuals but did not notice that. I have looked at the sight glass, but like a car A/C, figured that when too much refrigerant is lost, the cooling will suffer. Then will be faced with getting some R-12 off eBay and having it recharged or buy the new compressor. My (car) mechanic recharged our old 325iX with a can I bought and it's been fine for two summers now. He says he can clean out the compressor and upgrade the refrigerant w/o buying a new unit. Deal with that when it happens! The shore-power unit does not work but then I'm never plugged into AC while on the water.