Defective or worn-out parts often cause a refrigerator to run all the time even after turning the control down. For instance, if the defrost heater assembly or defrost thermostat is not functioning properly, frost builds up on the coils.
A damaged or faulty door gasket prevents the refrigerator door from shutting tightly. Warm air enters freely, and the defrost cycle must work overtime. Also, if the evaporator fan motor works poorly, cold air does not circulate sufficiently.
The condenser fan motor helps cool the condenser coils, but the refrigerator does not shut off if the motor is flawed. The same problem occurs if something becomes lodged in the condenser fan motor blade. Dirty condenser coils also make the appliance run continually.