Freezestat 

A freezestat is a device that controls the temperature of a refrigerator or freezer. It is typically used in commercial applications, such as supermarkets, where large quantities of food need to be kept at a consistent temperature. The freezestat is usually mounted on the outside of the fridge or freezer and is connected to a thermostat inside the appliance.

When the temperature inside the fridge or freezer exceeds the set point on the freezestat, the device will turn on the cooling system to bring the temperature back down to the desired level.