That's a new one on me.... I'm not sure I understand why you would do this. If the system is sealed, it should be ok for many, many years. Has it been discharged and open for a while? Even so, I don't know why it would be necessary. I had one unit of my two unit system compressor die and I didn't get it repaired for almost 9 months. The repairman replaced the compressor, installed a suction filter and pressure filter and started it up. It's been running fine for years now.