No frost refrigeration units are designed to cool a space without formation of ice in the evaporator since ice could hinder the heat absorption of refrigerant. This is done by automatically defrosting method and the used of blower to move air inside the evaporator compartment. The sequence of operation is controlled by a device called defrost timer. Due to the presence DT in the circuit, wiring connections has changed.
The above figure shows the wiring connection of no frost refrigerator (defrosting mode). DT serves as a relay to change the operation into defrosting or cooling mode which is also controlled by the thermostat. DT has a coil to run the mechanical gear inside to close and open 2 and 4 terminals at given time. Defrosting mode is also dependent on the action of thermistor or defrost initiation switch that closes only when there is a build up of ice in the air passage inside the evaporator compartment. When thermistor closes, defrost heater melts the ice.
During cooling mode, current from L1 passes through the thermostat to the terminal 1 of the DT, 1 connects to the terminal 4 to supply power to the EFM and common terminal of the compressor where OLP is also placed. Running terminal of the compressor and other terminal of the EFM gets power from L2 to complete the circuit.