The constant temperature reset type temperature controller is also called constant on type thermostat, and the actual shape is shown in Figure 5-13. This temperature controller is only used in a direct-cooled two-door dual-temperature or single-temperature control refrigerator, usually placed in a refrigerating compartment, and the temperature sensing tube is in contact with the refrigerating compartment evaporator. Regardless of the temperature of the refrigerator shutdown, the startup temperature is always constant. Generally, the temperature of the evaporator of the refrigerating compartment rises to about +5 °C after each shutdown, and then the evaporator of the refrigerating compartment is always kept frost-free.

This temperature controller uses a temperature sensing tube to sense the temperature of the refrigerator compartment evaporator. Its shutdown temperature is related to the position of the thermostat knob, and the startup temperature is fixed, generally +4.5 °C ± 1.5 °C.
Figure 5-14 shows the internal structure of the temperature-reset type temperature controller.

The basic structure and working principle of the constant temperature reset type temperature controller are basically the same as those of the ordinary type temperature controller. Its characteristic is that the shutdown temperature can be adjusted by adjusting the temperature controller knob, but the startup temperature remains unchanged (usually 4.5 °C ± l °C) regardless of whether the set control point is at the strong cold point or the weak cold point. When the temperature of the temperature sensitive agent in the temperature sensing tube installed on the surface of the evaporator of the refrigerator compartment rises above 0 °C (4 to 5 °C), the compressor can be re-energized. So that the frost layer on the secondary evaporator can be completely melted during the compressor downtime.
The characteristic parameters of the common refrigerator temperature controller are shown in Table 5-1. At normal temperature, the temperature controller's switch should always be on (except for the knob to the forced shutdown position). Otherwise, the temperature controller is damaged. The cause of the damage is generally a leak in the temperature sensing tube or a poor contact due to contact oxidation.