A new approach for the thermodynamic analysis of vapor compression refrigeration machines, first presented by the authors at the IIF/IIR Conference in Sofia, Bulgaria (1998), is here both improved by removing some simplifying assumptions and applied to an existing and operating refrigeration plant in order to achieve the following objective: to test its capability to predict the performance of such machines both at design and at off-design conditions, by comparing with experimental results. This is a very important step since a high prediction capability allows the developed analysis to be used not only for performance evaluation, but also for design purposes. In particular, once the refrigerant, the secondary fluids, and the geometry of the machine are known and the operational parameters are given, the proposed thermodynamic model predicts the coefficient of performance (COP), the refrigerating power and the other important operating conditions of the vapor compression equipment.