Toyota Repair: 94 Camry Aircond problem, pumb, orifice tube

Question
My car has 130K miles; for the last 10K, the air cond hasn't worked properly. It starts off cold for 5 minutes or so, then quits. I and my mechanic have check the freon level; it's OK. The AC will not work for 20-30 minutes, then it starts again for 5 minutes only. My mechanic (not a detailed AC guy) says that the high side  pressure builds to 500psi and the system is probably protecting itself and prevents the pumb from working. With the engine off, it takes quite a while for the high side pressure to come down. sounds like a blockage somewhere. but where and what are the possibilities? Thanks

Answer
Hi Roger, mostlikly is the orifice tube. your best bet is to take it to a/c specialis and do it properly. when a/c compressor start to wear smal pieces can plug the orifice. or if moisture gets in to system and your drier is old and not doing its job anymore there are acids that are destroing the aluminum. Hope is something minor!