An experiment was initiated to examine the extent of component separation in refrigeration systems using HFC mixtures. The working fluid used was R407C, a ternary mixture of R32, R125 and R134a which has attracted attention as a replacement for R22 in a variety of applications. The test was designed to examine the two basic system configurations, namely dry-expansion and flooded evaporator, by incorporating an accumulator at the exit of the evaporator. A non-soluble lubricant was used to ensure that changes in composition were not attributable to differential solubilities of the component fluids. The composition of the circulating fluid was observed to be close to that of the charge composition while the system was operating in dry-expansion mode. Where the evaporation process was incomplete, an accumulation of fluid in the reservoir between the evaporator and the compressor caused the circulating fluid to become enriched in its more volatile components. The extent of composition change is dependent on a number of parameters, the most important being the charged mass, the internal volumes of the system and the compositional relationships of the component fluids.