Replaced compressor with 404A rated compressor. Weighed in charge and have some questions. I am at about 40-60 degrees superheat and still having frost on the suction line at the compressor. I am assuming it is because the vapor temperature is so cold and not that any liquid is coming back to the compressor. With a superheat I don't think I am getting any liquid back. Is this normal? Don't have any idea how this operated before as the compressor was junk when it got here. What am I looking for in charging this system?