The correct way, is to recover the refrigerant that is in the system. Then disconnect what ever needs to be undone. After replacing whatever needs replacing, add the correct amount and type oil to make up for the oil lost from a leak or replacing components. Connect the system back up using new "O" rings and/or gaskets, and drier. Evacuate the system using a good vacuum pump. Then add the correct amount and type of refrigerant. If the system has had a mechanical failure, or has been empty for an extended length of time, the system should be flushed.
