A/C not working

I have a 2005 Prius with 55k on it and I noticed that the A/C stopped working a month ago with no noise or any indication. I scanned threads on this site and checked the fuses and the freon level and looked for codes and there weren't any. I decided to save time and took it to the dealer and had their ace Prius mechanic work on it. He couldn't find anything wrong, so he contacted Toyota and they thought it was the inverter. They put in a known good inverter, and still no A/C and I was out 3.5 hours labor at $130/hr! Toyota next told the mechanic to replace the compressor ($1000 for the part and another 3.5 hours labor!!!) to see if that would maybe fix it. The mechanic felt bad and tried out an A/C amplifier from his 2004 Prius on his own time to see if that would fix the problem, and it did not. I don't mind paying to fix something, but I seem to be going broke on a fishing expedition. They tell me there is no way to test the compressor without replacing it? Is this true? Does anybody have any ideas out there for fixing this? Thanks in advance