| 摘要 |
PURPOSE: To accurately detect the frost formation of a heat exchanger by a method wherein an average value of temperatures at a plurality of places of a heat exchanger where the evaporation temperature of refrigerant is lowered is obtained and it is used as the criterion for judging the frost formation of the heat exchanger. CONSTITUTION: The temperatures detected by a first restrictor 7 and a second restrictor 23 are sent to a control device 27 as temperature signals and the control device 27 calculates an average value of the temperatures calculated from these detection signals. The calculated average value is compared with a predetermined frost formation temperature to judge whether or not it exceeds this frost formation temperature. The frost formation temperature is previously input in the control device 27 due to connection with external temperature. If the control device 27 judges that the average temperature is not higher than the frost formation temperature, a switching signal is sent to a four-way valve 11 to switch refrigerant passage so as to perform defrosting operation for a predetermined time. After the defrosting operation, the control device 27 again switches the refrigerant passage by the four-way valve 11 to restart the heating operation. By such defrosting operation as this, the frost is removed from a heat exchanger 9. |
