| 摘要 |
PURPOSE:To start a defrosting operation at a constantly appropriate frosting quantity by issuing a defrosting starting instruction based on three points, i.e. the temperature of a heat source side heat exchanger, the temperature of external air, and the temperature of a utilizing side heat exchanger, and issuing a defrosting terminating instruction when the temperature of the heat source side heat exchanger has reached a predetermined value. CONSTITUTION:An electronic control part 12 comprises a circuit for issuing a defrosting starting instruction at three points, i.e., the temperature TR1 of the heat source side heat exchanger, the temperature TA of external air, and the temperature TR2 of the utilizing side heat exchanger, a timer circuit for securing a minimum heating time, a timer circuit for determining a maximum defrosting time, and a circuit for issuing a defrosting terminating instruction when the temperature TR1 of the heat source side heat exchanger has reached a predetermined temperature regardless of the temperature of external air. The defrosting start (indicated by a straight line 40) is determined by the temperature TA of external air the temperature TR1 of the heat source side heat exchanger and the temperature TR2 of the utilizing side heat exchanger. The defrosting termination (indicated by a straight line 2) is determined by setting the temperature TR1 to a predetermined value regardless of the temperature TA of external air and the temperature TR2 of the utilizing side heat exchanger, and the defrosting starting 40 is set at a value a little before a point 4a in Fig. 1 up to which the temperature TR1 of the heat source side heat exchanger is lowered.
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