1995 Buick Lesabre No air flow

Air Conditioning problem
1995 Buick Lesabre 6 cyl Front Wheel Drive Automatic 104k miles

I get air flow from the vents for about 2 minutes after I have going down the road for a few minutes. After that I get no air flow at all including the outside air. I have put in about 2 pounds of freon including some oil, dye (don't see a leak) and stop leak but that didn't help. A friend had said there is an orfice that needs to be replaced but I don't know.