During the defrost cycle I can hear a load hum and sometimes a "whining" sound. The cycle seems to last too long allowing the temp in the freezer to reach 40 degrees. The cycle ends and the compressor kicks in. Everything in the freezer thaws out a little; ice cubes melt and then re-freezes. I have replaced the following: All of the thermistors (in the freezer and the fridge side), the evaporater heater, the thermostat, and the main mother board. I am at my wits end. I have cleaned the coils and checked for obstructions in the drain tube. Everything works fine until the defrost cycle kicks in.
What else should I check? Is it possible that the evaporater fan motor is bad? Or maybe the main board was defective when I got it?
Any help will be much appreciated.