The aim of this study is to show how to use the p-h diagram successfully for diagnosing faults in the vapor compression refrigeration cycle. This new approach is able to remove the gap between the information required to apply a general theory of diagnosis and the limited information on the p-h diagram. With this approach, an expert may interpret more failures of the refrigeration systems. In this study, an experimental setup with eight artificial faults was used to demonstrate the implementation of diagnosis. It is approved that with the assistant of cycles on the p-h diagrams, the difference between normal and faulty conditions can be easily observed. (C) 2014 Elsevier Ltd and IIR. All rights reserved.