2006 Mazda 3 Intermittent Air conditioning

Problem getting progressively worst. Last year, push the air conditioning button and get green light on switch and cold air. Every once in a while green light would go out and I would not get cold air, but problem would go away. Now, I push button and get green light and no cold air.....for first 10 to 12 miles, and then all of sudden it starts blowing cold air......it will blow for 6 to 8 miles and then go off and start blowing warm air again. Thank you.