A refrigerant charging system for charging a refrigeration system with refrigerant includes a refrigerant source, a storage vessel, input and output lines, and a device for detecting mass of refrigerant within the storage vessel. The input line fluidly connects the refrigerant source to the storage vessel, and the output line extends from the storage vessel and is adapted to connect to the refrigeration system. The system also includes an input control valve disposed between the storage vessel and the refrigerant source, and an output control valve disposed between the storage vessel and the refrigeration system. A heater is connected to the refrigerant source for raising the temperature of refrigerant within the refrigerant source. A method of charging a refrigeration system is also disclosed. The system and method are useful to charging the refrigerant system of an automotive vehicle, among others.