In this paper, a numerical model is presented for predicting capillary tube performance using new alternative refrigerants to HCFC-22. The model has been established after the fluid flow conservation equations written for a homogeneous refrigerant fluid flow under saturated, sub-cooled and two-phase conditions. Numerical results showed that the proposed model in question fairly simulated our experimental data and fairly predicted the capillary tube behaviour under different conditions. The results also indicated that a system using R-407C would experience smaller pressure drop compared to R-410A and R-410B. Copyright (C) 2000 John Wiley & Sons, Ltd.