Abstract: Apparatus for analyzing air conditioning systems comprising a temperature probe adapted for manual placement at each of a plurality of preselected points in turn around the refrigerant loop to provide signals indicative of temperature at each point. Apparatus electronics are coupled by a cable to the temperature probe and includes facility for reading and storing each of the probe temperature measurements in turn. Information indicative of standards and ranges of temperature data for properly operating refrigeration systems of a number of models and manufacturers is prestored in apparatus memory. The system temperature readings are compared to each other and to the prestored data to diagnose a plurality of fault conditions and to display diagnosed fault conditions to an operator.