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 arti-
ficial 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.