In this paper, an experimental study is presented to enhance our understanding of the capillary tube behaviour using some new alternative refrigerants to HCFC-22. An experimental setup fully instrumented was used to gather the behaviour of three different capillary tube geometries with R-410B, R-407C, and R-410A under various conditions; saturated. sub-cooled and two-phase. Experimental data showed that R-410B has the highest pressure drop along the capillary tubes compared to the alternatives under question and also has the highest temperature drop along the capillary tube. The data also showed that R-407C has similar capillary behaviour to that of R-22. The results clearly demonstrated that the pressure drop is significantly influenced by the diameter of the capillary tube, the type of refrigerant and inlet conditions to the capillary tube. The data also showed that the capillary pressure drop decreases with the increase of the capillary diameter. There is clear evidence that the component concentration of the refrigerant mixture significantly affects the capillary tube behaviour and particularly the pressure drop along the capillary tube length. Copyright (C) 2001 John Wiley & Sons, Ltd.