In this study, the effect of using phase change materials on the air-conditioning system energy consumption of a typical room in a multi-floor building has been studied using EnergyPlus software. As the melting point of PCMs has an important impact on their effectiveness, as a part of this research, the effect of Iran climatic conditions on the appropriate melting point of the PCM has been investigated in 4 cities: Tabriz as a cold, Tehran as a moderate, Yazd a dry-hot and Bandar-e-Abbas a humid-hot climate. Based on the results, the proper temperature of PCM melting temperature is between 21 to 27°C and the saving varies from 1.6 to 13.2%. The results of this incestigation are useful in getting better understanding of the effect of PCMs on reducing the HVAC system energy consumption and in determining the PCM appropriate specifications.