Your not going to like what i have to say.... sounds like non condensibles to me if you keep adding refrigerant and the flash point continues to freeze. and suction pressure don't move
Dont feel bad i just flushed evap and condenser, changed accumulator,orifice tube,flushed,vacuumed,leak checked, had it blowing out 47 degrees with 134A yesterday and the compressor went out last night.BTW that's what you need to do, change that accumulator .It sounds like it has moisture saturating it and no matter how much you vacuum on a 30 year old car it will have moisture in the system .It will never work correctly .also when charging make sure you purge the lines of air to confirm nothing but refrigerant goes in the system.all my parts at Rock auto were 31 dollars plus the flush 16 dollars .... i have a 30 lb jug of 134 and a flush gun.if you buy small cans you will have about 100.00 total if you shop