The 1 most common part(s) or condition(s) which cause the symptom Refrigerator not defrosting are listed below starting with the most likely. Check or test each item and watch any available videos.
RepairClinic Item # 1515046
If the refrigerator is not defrosting, the main control board might be defective. A few times a day the control board is supposed to turn off the cooling system and turn on the defrost heater to melt away any frost that may have accumulated on the freezer evaporator coils. If the control board is defective it could cause the system to never cycle into defrost.