Samsung RF26J7500SR/AA-04 defroster not working

[tbenn]

Hi All - 

Last year I noticed my fridge making some noise. After some diagnostic and disassembly I saw that the interior fan was hitting ice and that the entire evaporator coil was covered in a block of ice. I let the fridge defrost over night and reassembled the fridge and it worked fine for a few months and then it continued to ice over again. I've gone through this process several times now and I'm looking for a permanent fix. 

I tried to replace the heater coil in the fridge with a brand new coil and it doesn't seem to be working. I let the fridge run for 24 hours and then I tried to put the fridge in Forced Defrost mode but the coil never gets hot. I suspect that there might be something failing to supply power to the heater coil but I'm not sure what to replace or how to debug further. 

When the fridge was in forced defrost mode, I took a voltage detector pen and put it across the brown wires that supply voltage to the heater and it did not detect any voltage. 

Any help would be appreciated.