Air Conditioning problem in Firebird

I have a 2000 Firebird with about 100,000 miles. Last week my air conditioning was just fine until I switched it off for awhile.
When I tried it an hour later, it sounded the same but it blows warm air. I think it's the same as the outdoor temperature, the only difference is it seems to feel like humid air.
Does that sound like the symtoms of something specific or do I need a troubleshooting lesson?