what cone killer said. Take out orifice tube and flush that puppy out!!! Go both ways, backflush, up in the condensor, out the evaporator, any way you can flush it, do it. Look up the specification on amount and type of oil for your a/c system. Put a little in your compressor(so it is sure to have oil in it). Button it all up with new o-rings, and vac it down. The more air you get out, the better. Let the oil & 134a suck down, enjoy!!!

Why are you replacing a/c compressor again?