The efficiency of an ammonia refrigeration unit (ARU) depends on many factors. Changes of some of them result in thermal hydraulic oscillations arising within the system. They are caused by changes in ambient temperature, the performance of the compressor and condenser. All this leads to the pressure increase in the condenser and, consequently, to the excessive energy consumption, which is perceived as the presence of non-condensable gases (NCG) in the system. This brings about more frequent opening of NCG relief valves, resulting in a substantial loss of ammonia. Causes of the appearance and self-destruction of thermal hydraulic oscillations on the example of a large-capacity ARU are researched. To reduce these oscillations are developed and justified the new algorithms and modes of operation of the fan air cooling, which reduce the amplitude of the pressure fluctuations in the air condenser at 30 kPa (0,3 bar).