FREEZER

PROBLEM TO BE SOLVED: To reduce the cost of a freezer by dispensing with a differential pressure switch in a system of defrost control. SOLUTION: In the case of performing defrost operation, a condenser inlet solenoid valve 10 is closed through a condenser inlet solenoid valve relay 21, a defrost solenoid valve 11 is opened through a defrost solenoid valve relay 22, compressed gas refrigerant from a compressor is force-fed from a refrigerant pipe 30 through a drain pan heater 13 and a refrigerant pipe 15 to an evaporator 7, thereby defrosting the evaporator 7. The defrost operation is started in response to a defrost timer signal 18 or a manual defrost signal 19, or when a temperature difference Δt=t1-t2 between the internal temperature sensor t1 and a detected temperature t2 of a defrost end sensor 17 is larger than a designated value. When the temperature t2 of the sensor 17 becomes larger than the designated value, the defrost operation is ended. The differential pressure switch is not needed to reduce the cost. COPYRIGHT: (C)2003,JPO