A system and method for managing energy in large refrigeration systems and the like by continuously monitoring operating parameters and controlling to optimize the refrigeration system elements. A multiplicity of remote sensors is disposed at the appropriate points in the refrigeration system to produce analog electrical signals representative of various temperatures such as wet bulb temperature, dry bulb temperature, condensing temperature, evaporator air temperature, evaporator refrigerant temperature, and similar temperatures, and various pressures such as head pressure, booster suction pressure, intermediate suction pressure, and the like. A signal processor is provided to receive signals from the sensors, to condition the analog signals, convert to digital signals and to feed a digital computer which has a memory for storing system design parameters and refrigerant characteristics. The digital computer calculates the instantaneous system operating parameters from the digital signals, compares these parameters to the design parameters, and operates control relays to load and unload compressors to maintain optimum system pressures, to energize and deenergize fans and pumps in accordance with the system requirements, and to produce alarms when non-condensible gases and/or fouled condensers are indicated in the refrigeration system. In systems subject to frost build up on the evaporator, defrost cycles are also controlled by the computer to occur only when necessary.