2003 Chevy S-10 Air conditoner problem

Air Conditioning problem
2003 Chevy S-10 6 cyl Two Wheel Drive Automatic 89.000 miles

My air conditioner works sometimes. It will turn on right away most of the time then for no reason, just start blowing warm air. Then maybe a few minutes later it will come back on. Sometimes if I turn it off and turn it back on it will work again but not always. Then sometimes it will take a few minutes to start working when I first turn it on. Can you suggest what it might be I would sure appreciate it. Thank you.