My car's (2000 Seville STS) AC system had worked perfectly since I bought the car... until this morning!

Started the car, no cooling whatsoever (and I live in Florida, AC is not an optional thing for a black on black caddy!), went downtown for some errands. During the 3rd time I had started the car today, while driving down I-4 the AC starts cooling sudddenly (and it's blowing cold from all vents), when the compressor kicks off 10 minutes later the car gets warm again and now it won't kick back on.
I checked the AC fuse and relay, both tested good. Pulled codes, none stored.
Ideas? I'm thinking that the A/C clutch isn't engaging when told.