I took everything apart to get at the evaporator thermistor. Cut out that thermistor and all others 5 total. They all seemed to be within 10% of each other. I decided to replace all thermistors, main board, climate control drawer board, defrost heater and heater cut-off. (1K of parts). Frig has been working properly for a month now. I'm thinking the climate control drawer board which had not been working (no led lights coming on) was blowing out the main board which I had replaced twice and frig was still icing over at the evaporator. Or maybe the frig. will not work without the climate control drawer board working properly. Anyway I'm keeping fingers crossed frig. continues to work properly.