Abstract: Temperature and threshold parameters relating to the cooling system are received. A control condition suitable for the cooling system is determined. If the ambient temperature is lower than the first temperature threshold, the working fluid passage between the free cooling device and the system to be cooled and the working fluid passage between the free cooling device and the PCM cooling device are turned on, in addition to the PCM cooling device is set into the first working mode. If the ambient temperature, AT, is higher than the second temperature threshold and the temperature of the PCM material is lower than the melted state temperature threshold, the working fluid passage between the PCM cooling device and the system to be cooled is turned on, the working fluid passages relating to the free cooling device is turned off, and the PCM cooling device is set into the second working mode.