Household refrigerators mostly use mechanical vapor compression refrigeration systems that are comprised by four basic components: condenser, evaporator, compressor and expansion device. These systems use a refrigerant fluid, which is a stable and inert chemical compound that, depending on the temperature and pressure conditions, undergoes a phase change process with high rates of heat transfer. There are several types of refrigerants available, for several applications. Currently, R134a and R600a are the most used refrigerants in domestic appliances. The refrigerant load, or charge, strongly affects the power consumption of small refrigeration systems. Lack or excess of charge, and the incorrect combination with the expansion device, adversely impacts system performance. The refrigerant load is strongly dependent on the four basic components of the system and it is a function of external and internal temperatures. Methodologies for the optimization of refrigerant charge are widely studied and used in POLO. The laboratory has an automatic device for refrigerant charge determination, consisting of a cylinder suspended in a load cell and two direct-action solenoid valves, which are able to insert or remove refrigerant with an uncertainty of ±0.3g. Thus, it allows easy identification of the optimal charge for each refrigeration system and further evaluation of its sensitivity to different operating conditions.