PURPOSE: To change over a defrosting operation after sensing a discontinuity into a duty controlling operation by a method wherein a defrosting control device is provided with a control means for completing a defrosting operation of a defrosting heater when a discontinuity sensing device detects a discontinuity of a temperature sensor and receives an abnormal signal and at the same time for changing the defrosting operation of next time into a duty controlling operation.
CONSTITUTION: A discontinuity sensing device 20 is provided with a discontinuity sensing resistor 27 connected between a controller 15 and one input terminal of a comparator 26. The controller 15 outputs a low potential signal (an L signal) during a defrosting operation regularly as a discontinuity confirmation signal and performs a sensing of the discontinuity of a thermistor 21 in response to an output from a comparator 26. In this case, when the output form the comparator 26 under an output of the discontinuity conformation signal is an L-signal, the controller 15 judges that the thermistor 21 is broken and completes the defrosting operation an then the defrosting means 12 is changed over from its normal continuous electrical energization operation to the duty controlling operation under the operations of the first to fourth timers 16 to 19.
IWAMOTO MASAYUKI
YAMAGUCHI TATSUHIKO
