Abstract: A device for monitoring the physical and thermodynamic states and concentration of components of a fluid mixture within an operating refrigeration system to detect precursor conditions of system malfunction. Monitoring and detecting refrigeration system fluids is accomplished by continuously sampling the fluids at critical positions within the system during operation. The sampling is accomplished by means of a plurality of sensors positioned within and adapted to detect changes in the heat constants of the fluids. Electronic circuit means utilizing voltage signals derived from the sensors discriminates between normal operating conditions and malfunction precursor conditions. The electronic circuit output is applied to control operation of the system to prevent system damage and to actuate the system status visual display.