If your refrigerator freezer is not defrosting, or your refrigerator is not cooling, it could be due to a bad defrost thermostat.
The defrost thermostat detects the temperature of the evaporator coils inside the freezer portion of a refrigerator. Cold air from inside the freezer is then pushed into the refrigerator. When the temperature of the evaporator coils drops, the defrost thermostat turns on and allows power to flow to the defrost heater. The defrost heater then melts the frost and ice off of the evaporator coils, allowing the proper temperatures to be maintained in your freezer and refrigerator.
If the defrost thermostat stops working, then the defrost heater never turns on and melts the frost on the evaporator coils. This can cause the coils inside the freezer to ice up and stop producing cold air.
To determine if the defrost thermostat is defective, use a multimeter to test the part for continuity. Purchase a new refrigerator defrost thermostat at EveryAppliancePart.com.
WARNING! Before attempting to work on any appliance, make sure that all power (electricity) and utilities (water and gas) have been turned off and/or disconnected on the appliance. Read this before you start any repair.
You may need to remove shelving, shelf supports, drawer slides, screws and refrigerator panels in order to reach the refrigerator defrost system housed inside the freezer.
Once the panel is removed, find the defrost thermostat. Sometimes the defrost thermostat is held to some tubing using a clip. If so, unclip the part from the tubing, first before cutting the wires close to the defrost thermostat in order to remove the defective thermostat from the refrigerator.
You may need to strip back some of protective insulation wiring cover in order to attach the new wiring from the new part. The new defrost thermostat should come with two vinyl butt splice connectors which can be used to attach the wires from the new thermostat to the refrigerator. Crimp the butt connectors closed over the new wire connections.
Place the heat shield tubing or heat shrink wrap over the butt splice connectors in order to protect the connectors from moisture. Use a lighter or heat gun in order to shrink the wrap around the connectors.
Reattach the spring holding the defrost thermostat to the tubing. Replace and reinstall all panels, shelving, shelf supports, drawer slides, and screws.