The system is in the mode of initial rapid cooling and the defrost thermostat contacts are set to the position corresponding to the warm evaporator. The compressor is powered via the defrost thermostat, while the fan is de-energized.
The system operates in this mode only for several minutes. Usually this time is enough for sufficient cooling of the evaporator and switchover of the defrost thermostat contacts to the right-hand position according to the diagram, corresponding to the cold evaporator.
The evaporator has cooled down sufficiently and the defrost thermostat contacts have switched over to the right-hand position according to the diagram.
The compressor is now powered via the defrost thermostat and the timer connected in series. The fan is still de-energized, but the timer will power it up in several minutes.
The timer contacts set to a position providing simultaneous power supply of the compressor and fan. It is the main system operation mode, in which it stays for the next few hours, cooling products in the refrigerator boxes.
The timer motor is powered via the defrost heater.
The system has set to the defrost mode. The timer de-energized the compressor and fan and powered up the defrost heater.
Evaporator temperature is low as yet, that’s why the defrost thermostat contacts are in the right-hand position according to the diagram. The timer motor is de-energized. Evaporator temperature slowly rises due to heater operation.
The heater warmed up the evaporator to above the frost melting temperature and the defrost thermostat contacts have switched over, de-energizing the heater and powering up the compressor. The timer motor is also operating. However, the fan is still de-energized.
We see there is no pause. The system activates the compressor right after heater switch-off. While the system operates with the compressor ON and the fan OFF, the cooled evaporator successfully recovers the heat generated during defrost.
The system operates in this mode for several minutes, and then the timer will switch over its contacts.