Cold storage

1. A cold storage comprising:

a box having a cold storage chamber;

a compressor constituting a refrigeration circuit that cools an inside of the cold storage chamber;

a defrost heater that heats an evaporator constituting the refrigeration circuit; and

a control apparatus that controls the compressor and the defrost heater,

wherein the control apparatus operates the defrost heater when the compressor is not operated,

when an outside air temperature is equal to or higher than a chamber temperature in the cold storage chamber, the control apparatus operates the compressor upon the chamber temperature rising up to a first threshold and stops the compressor upon the chamber temperature dropping down to a second threshold lower than the first threshold, and

when the outside air temperature is lower than the chamber temperature, the control apparatus does not operate the compressor until the chamber temperature rises up to a third threshold higher than the first threshold, and the control apparatus operates the compressor when the chamber temperature reaches the third threshold.

2. The cold storage according to claim 1 ,

wherein, when the outside air temperature is lower than the chamber temperature, the control apparatus operates the defrost heater upon the chamber temperature dropping down to the second threshold.

3. The cold storage according to claim 2 ,

wherein, when the outside air temperature is lower than a set temperature for the cold storage chamber, the defrost heater generates an amount of heat enough to raise the chamber temperature up to the set temperature.

4. The cold storage according to claim 2 ,

wherein the control apparatus stops the defrost heater such that the chamber temperature becomes lower than the third threshold.