Defrosting is generally time-controlled, i.e. it occurs e.g. every six, eight or twelve hours. The end of the defrosting process is normally determined when an end temperature is reached at the defrost end sensor above the air cooler. At the same time, however, a maximum defrosting period is also specified. If this is exceeded, defrosting is also terminated.
Some controllers are able to carry out defrosting as and when required. In this case, defrosting is triggered if the supply air temperature is not reached over a specific period or if the temperature differential between the supply air and the return air is too high. Both criteria can indicate an insufficient air flow, which could in turn be caused by ice formation on the air cooler. Other causes are also possible, however, making it difficult to carry out defrosting automatically as required.