The subject of this work is diagnosis of failures and maintenance of the ship's refrigeration system. The cooling process is a process in which the temperature of space or its contents decreases below its environment. Cooling is used to transport some liquefied gases and bulk chemicals in air conditioning systems, fire protection systems and the preservation of flammable food products during food transportation. At the beginning of the nineteenth century there was a successful attempt to transport some of the foodstuffs by boat at short distances. By constructing steam dampers and testing several chemicals that were supposed to replace air as a coolant, the formation of marine cooling systems and their mode of operation began to develop. Only with the discovery of some of the newest optimal cooling agents is the development of the refrigeration industry or the expansion of the cooling technology on board. For high quality diagnostics and system management it is necessary to know its structure, connectivity and interdependence between subsystems and components, and continuous monitoring of work and changes over time, ie a quality and comprehensive real-time monitoring system to which the diagnostic and maintenance system is complemented.