I had an odd experience this afternoon, too. I decided to celebrate the 80 degree temp by driving home with the A/C on. So I turned the switch, but no cold air. I drove for a few miles until I stopped at an intersection. When I started up again the A/C came on like always. I haven't been using the A/C this spring since I got the sunroof installed.
There was no noise like squealing or anything it just started up.
Think maybe the compressor is annoyed at the sunroof?
-Jim