1968 98 a/c problem

i had great a/c in june. the hoses leaked so i had them restored.took a month .put the hoses back on,had my mechanic evacuate charge it up r "12" worked great 40 degrees..drove 10 miles came home parked it ,2 hrs later got in it put a/c on nothing.the exp valve was frozen the suction side hot. ok we change the expansion valve (all parts are orginal ) charge it up ,same thing.poa giving me 20 lbs with a full charge.now what ??change poa??,when u first put it on starts to get cold then levels off a 60 degrees...