| 摘要 |
PURPOSE:To carry out a defrosting operation appropriately by composing a control circuit of a temperature detecting part, a pulse generating circuit, a frequency dividing circuit, a preset counter, a preset pulse generating part and a reset pulse generating part. CONSTITUTION:When a switch circuit 7 is excited, an exciting coil 8 of a four- way valve connected in series with contacts of the switch circuit 7 is deenergized and the flowing direction of a coolant is reversed, so that the temperature of an exterior heat exchanger is raised to melt the frost. When the frost is melted completely and the detected temperature reaches a reset temperature or 10min of defrosting period is elapsed, an AND gate 6 is not made to be valid and the defrosting operation is finished. This information is readily transmitted to the reset pulse generating circuit 9, whereby the pulse oscillator 3, the frequency dividing circuit 4 and the preset counter 5 are cleared and the counting for a heating period is restarted. Then, preset pulses are generated by the preset pulse generating circuit 10 and are added to the counter 5. |
