The first thing you want to do is open the freezer and see if the fan inside there is running. The reason is the freezer cools the refrigerator side by circulating air from the freezer. If the fan is running then your problem is one or more parts of the defrost system is malfunctioned and in return your problem arises. There are three parts to the system, the defrost timer or in some cases control board, defrost thermostat also known as a bi-metal, and the defrost heater. The defrost system is set up to operate as so. The defrost timer or control board will turn the machine off, in some cases every 8 hours, some 12. During this time period the defrost heaters, located behind the freezer wall and rest underneath the evaporator, yet wires to them run up the side of it, are energized and emit heat that raises upward to melt the ice that has formed on the evaporator coils. The bi-metal or defrost thermostat is at the top of the evaporator. When the heat from the heater starts to reach the bi-metal, it breaks the circuit turning the heater off. The whole purpose of this is because the freezer cool the refridgerator side by drawing air across the coils and blowing to the other side via the evap fan motor. In my opinion, if you change one part of the defrost system change them all because usually when one part fails another will follow, so save yourself the time and the food loss, the cost difference is minute.
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