Abstract This paper has arisen from a project which aims at developing a microcomputer-based fault-diagnostic instrument, for use with respect to the behaviours of most forms of refrigeration plant. The initial stage in the development of such an instrument is to compile a suitable software package, capable of calculating certain refrigerant and cycle properties from simple pressure and temperature inputs, at the four state-points of the cycle. This has been achieved using a BASIC program which can determine the following: • • the thermodynamic properties at the cycle state-points; • • component energy balances; • • isentropic efficiency of compression; and • • coefficient of performance. By evaluating the various arbitrary constants required in the equations used within the program, it is possible to estimate the properties of refrigerants R11, R12, R13, R14, R22, R113, R114, R500 and R502 as functiions of their characteristic parameters at any state-point. All the derived equations and characteristic constants are collated and presented in this paper. The computed properties of the refrigerants have been compared with pertinent published data, and the presented correlations provide good degrees of agreement between the calculated values and published data.