Our goal in this work is the development of a tool of calculation of the thermodynamic properties of the refrigerants (pure or in mixture) the more used in the domain of the refrigeration and air conditioning. The choice of the parameters to define carried itself on the domains vapour and liquid of the refrigerants. Indeed, it is the two domains that have the more of interest for the calculations of the refrigeration’s machines. The knowledge of these equations allows to reach, after calculation, the parameters of state of the fluid (the P pressure, the V volume, the S entropy, the enthalpy H, etc.), who will be used then in calculations of the refrigeration’s cycles. This work includes in addition to the development of the calculation tool, a research of the equations of state and the available mathematical models currently permitting to produce the thermodynamic properties of the fluids selected for the survey as faithfully as possible. For the choice of the state equation, we proposed the equation of state of PENG-ROBINSON, with two parameters, of which the term of attraction has been conceived in the goal to represent the liquid volumes of the substances better to non spherical molecules. Our discussion carried itself on the results gotten after the use of PENG-ROBINSON’s equation by comparison to the results obtained by the software Cool Pack (version1.46).