CHEVROLET VENTURE AIR CONDITIONER BLOWS HOT

I Just Got The A/c Filled Up, On A 97 Chevy Venture 70,000 Miles. The 1st Five To Ten Minutes Works Good, After That Its Starts Getting...

My A/c Blows Hot Air Only In The Rear Vents. Any Suggestions. The Front Blows Very Cold So It Appears To Have Freeon And The Compressor...

The Air Started Blowing Out Hot Air, So I Added Antifreeze. I Turned On The Air And It's Still Blowing Out Hot Air. I Did This Before...