A system for deicing an external evaporator for heat pump systems includes at least one compressor, at least one internal condenser, at least one external evaporator, at least one liquid separator, and a system of ducts for cooling fluid. The deicing system includes a secondary refrigeration circuit, which includes a tank for storing a heat transfer fluid, and a first heat exchanger immersed in the heat transfer fluid and adapted to transfer heat to the heat transfer fluid by cooling the cooling fluid. The system further includes a bypass refrigeration circuit, which includes the tank, and a second heat exchanger immersed in the heat transfer fluid and adapted to absorb heat from the heat transfer fluid by heating the cooling fluid. The system also includes a deicing circuit adapted to convey cooling fluid.