Charging a refrigeration system is one of the most challenging and puzzling tasks a service technician will face. How much refrigerant a technician should put into a system when charging is a tough question to answer, because it is often system-dependent. If there is no nameplate specifying the charge amount in ounces and pounds, there is really no straightforward answer, because all refrigeration systems differ in the amount of charge they hold. This is especially true for field-assembled refrigeration systems in which liquid and suction line length and size can vary considerably.
Nameplates sometimes specify charge amounts on smaller unitary systems. If the charge amount is specified, a technician is sometimes better off recovering the entire charge, servicing and leak-checking the system, pulling the desired vacuum, and charging the nameplate amount of refrigerant into the system. This method leaves no guesswork as to whether the system is properly charged. This is assuming that all lines and accessories are properly sized to factory specifications.