Replaced mother board in August 2011 and this morning freezer was iced over in back and temp was warm I defrosted coils and compressor came on so figured it was the defrost cycle. Heater looks black but checks 22 Ohms, the thermostat clipped on coils shows closed at room temperature. I am thinking it is the mother board and made a call to Appliance repair and they are sending me another Mother Board but just wanted a confirmation from you experts that that is what the problem is.. Do you think I should replace heater just for insurance for future or just use it?

With the refrigerator running, unplug and remove motherboard cover. Locate the gray, three pin connector and remove it. Place a wire jumper between the two mating pins that match the motherboard pins labled line and def. Plug fridg in, if you now get defrost action, youi have a bad board, if not, probably a bad defrost thermostat.