This paper reports on a numerical model derived to predict the transient thermohydraulic behavior of the air and refrigerant in a heat exchanger for refrigerant systems. The purpose of this study is to improve the numerical model of the fin-and-tube heat exchanger for air conditioners. The equations of mass, energy, and momentum were completely separated for vapor and liquid in a two-phase thermal fluid flow. The model was validated by analyzing experimental data based on the temperature and pressure of the refrigerant. The numerical results of superheating, temperature, and pressure distributions in each zone in the fin-and-tube structure were estimated using the input variables. The maximum errors in temperature difference and pressure were within 5 degrees C and 4%, respectively. (C) 2015 Elsevier Ltd. All rights reserved.