Abstract: The invention relates to a refrigeration unit of the type having a vessel for cooling water and a heat exchanger for the liquid to be cooled mounted in the vessel. Evaporator tubing is mounted on the inner wall of the vessel and a sensor mounted a predetermined distance from the tubing monitors the formation of an ice layer on the tubing. Control regulation which prevents both freezing and undesired heating of the cooling water is based on controlling the compressor providing first and second temperature ranges associated respectively with first and second sequentially generated time periods.