Unplug the fridg, remove the motherboard cover and the four pin power connector. Match the power connector pins to the mating pins on the motherboard and jumper connector pins labled "line and defr." Plug in fridge. If still cold, your fridg should now start to defost. If not, you have a bad defrost thermostat, or defrost heater. If defrost, replace the motherboard and evaporator thermister. Parts needed AP4436216, motherboard, AP3185407, thermister.