Air Conditioning problem
1995 Lexus SC 300 6 cyl Two Wheel Drive Automatic 159000 miles

My ac is not throwing cold air at ALL. First i was told it was the ac compressor so i changed that and it had cold air for about a week. I was then told that it might need a recharge so i went to a shop and they said that it might be a clog. So I took it to another shop and they said that everything was fine, that it had freon, lines were clear, and that ac compressor was fine but they didnt know why cold air still wasnt coming out. Finally they said that it might be the vents from inside the car that was bad and that job requires taking apart the whole dash. If this is the problem, whats my next step or where should i take it to be serviced and finally fixed. Thanks