Freezer -26 evaperator runs constantly

[tcalla]

GE side by side: freezer section -26 degrees and fan runs constantly, refrigerator section appears to be OK 36 degrees. I called GE service for repair, repairman said the main board assembly was bad and would be $350 to fix but had to order the part. I ordered the board myself from APP part #AP3950129(GE # WR55X10552). I unplugged from wall and installed the board per included instructions. After waiting until evaparator coil to reach ambient temp, plugged it back in and set temp at 5 & 5. Let stabalize for 24 hours. Problem was not fixed, still minus -26. After searching forum I decided to remove cover and check the evaparator coil. It’s is completely frozen up. So checked defrost heater with DVOM ohms = 38, FF thermistor = 10.18 K ohms(indicates colder than ambient), FZ thermistor = 7.2 K ohms and Evaperator thermistor = 6.70 K ohms. Temprature at each thermistor was 63 +or- 0.5 degrees using digital thermometer. What could be the problem, I would prefer not to "Easter Egg" it by just replacing parts.