Refrigerating and air-conditioning apparatus

A refrigerating and air-conditioning apparatus comprising:

• a refrigeration cycle being constituted by connecting a compressor, a condenser, an expansion valve, and an evaporator, the refrigerant cycle performing a cooling operation;
• an evaporator heating device heating the evaporator;
• a drain pan receiving drain-water from the evaporator and draining the drain-water;
• a drain-pan heating device heating the drain pan;
• a frost detecting device including a light-emitting element that emits light to the evaporator and a light-receiving element that receives reflected light from the evaporator and outputs a voltage according to the reflected light;
• and
• a control device controlling on-off operation of the evaporator heating device, the control device preliminarily having a defrosting cycle ranging from a start of a defrosting operation to a start of a next defrosting operation,
• wherein, when a defrosting start timing of the defrosting cycle being reached, the control device
• obtains a frost layer thickness based on detection results of the frost detecting device,
• starts the defrosting operation when the frost layer thickness is greater than or equal to a predetermined frost layer thickness necessary for determining whether the defrosting operation is necessary or not,
• obtains an estimation value of a frost layer thickness at the next defrosting start timing on the basis of the detection result of the frost detecting device and a correction value when the frost layer thickness is less than the predetermined frost layer thickness, cancels the defrosting operation and continues the cooling operation when the estimation value of the frost layer thickness is less than the predetermined frost layer thickness, and
• turns on the evaporator heating device to start the defrosting operation when the estimation value of the frost layer thickness is greater than or equal to the predetermined frost layer thickness.