its freezing up because there is moisture in the system, when you replaced the compressor did you pull a vacuum on the system for about 30-45 min? if you just added refrigerant to the system then you also added moisture. the same goes for the guys that "top off" their systems. to do it properly any time the system is opened up (ex: replacing the compressor) moisture is introduced into the lines etc. through the air (there is always moisture in the air, thats where the humidity comes from) you need to pull a vacuum on it to boil the moisture out because if you dont it will form ice inside the lines when the compressor is running and eventually plug the lines up with ice until it quits working, you will see ice on the outside of the lines where ever the ice is on the inside. you shut it off the ice will thaw and it will work again until it fereezes up again. its also possible a piece of metal got stuck in the line along the way (from the failed compressor) and is causing a restriction that will also make it freeze up. my bets would be that there is moisture in the system though.
