A variable refrigerant charge refrigeration/air conditioner system is described that allows the refrigerant charge for the system to be altered based on operating or environmental factors. The system includes a main refrigerant loop holding a volume of refrigerant corresponding to a first level of refrigerant charge, a compressor in the main refrigerant loop, a condenser in the main refrigerant loop, and an evaporator in the main refrigerant loop. A branch refrigerant loop allows the alteration of the refrigerant charge using a control valve in the branch refrigerant loop and a receiver in the branch refrigerant loop. The receiver acts to hold a volume of refrigerant when the control valve is open, thereby removing the volume of refrigerant from the main refrigerant loop. A return path from the receiver to the main refrigerant loop allows refrigerant to flow back into the main loop from the receiver.