PURPOSE: To optimize the period or automatic defrosting operation for a cooler so as to conform to the condition of practical use and prevent wasteful consumption of electric power by providing a controlling means for controlling the regular period of starting the defrosting operation to be prolonged in the case where the operation rate of a compressor calculated by a calculation means is not higher than a preset upper limit value.
CONSTITUTION: After defrosting operation for a cooler 6 is finished, a calculation means 16 calculates an operation rate of a compressor 10 for freezing cycle drive. In the case where the operation rate or the compressor calculated by the calculation means 16 is not more than a preset upper limit value i.e., in the case where a rate at which the compressor 10 is operated is relatively low, so that the amount of frost produced on the cooler 6 is small, a controlling means 13 allows the regular period of starting the defrosting operation for the cooler 6 to be prolonged. As a result, when a state is such that the operation rate of the compressor is relatively low and the amount of frost to be produced on the cooler 6 is small, there is no possibility that the defrosting operation for the cooler is carried out in frequency more than necessity, whereby wasteful power consumption can be prevented.
TANAKA HIROSHI
KAWAMURA SHINICHI
YOSHIOKA ISAHIRO
