Evaporator fan quits after a few defrost cycles

Model Number: PSS26LSRE SS
Brand: GE
Age: 1-5 years

My freezer seems to get stuck in a state where the evaporator fan won't run, leaving the ice tray at the top of the freezer melting. I believe this is always happening after a defrost cycle. Whenever I reset (unplug and plug it in) the fridge immediately starts working properly, with the evaporator fan running and quickly cooling the freezer to single digit temperatures. It seems to consistently go through a defrost cycle or two of working properly, quickly cooling and running the evaporator fan after finishing the defrost cycle, just as it should. However, after about a couple days, it seems to go through a defrost cycle and the evaporator fan will never turn on again. The condenser will be running properly, and the evaporator coils are plenty cold, but the fan never turns on to cool the top of the freezer where the ice is.

I have replaced the defrost heater, thermostat, main board, and checked the thermistors, but the problem persists. In particular, I verified reasonable resistance levels (10-12K ohms right after defrost and it was a little above freezing, 25-30K after the condensor had run for a bit and it was well below freezing) from the plug directly at the main board (4th wire to 5th wire on the J1 plug). The fan seems to work properly after a reset, so I assume it is not a mechanical issue. It shows a resistance of 2.5K ohms from lines 3 to 8 on the J2 plug (and about 6K from lines 4 to 8). When the fan is running I see a voltage of 12.5v from line 3 to line 8 and 13.6v from line 3 to line 4. When the fan is "stuck", and not running, I see a resistance of 13.6v from line 3 to line 8 and from line 3 to line 4 (same potential). The defrost heater seems to work properly now that it has been replaced (glows during defrost cycle, defrosts the coils, and shows about 18 ohms resistance). At this point, I don't know what is left to replace or try to fix.

When the evaporator fan motor is working, do you hear it varying in speed? You can't do a voltage test on these motors because they operate using pulse width modulation. The presence voltage at the fan motor does NOT indicate that the fan motor should be running. Commonly what happens on these refrigerators is the fan motor goes bad and burns on the main control board. Replacing the main control board will making the fan motor start working again, but the new main control board will fail again because the fan motor is still bad. To fix the problem both the main control board and evaporator fan motor need to be replaced.

I replaced the evaporator fan, and over the last week or so, we haven't experienced any problems with the freezer getting stuck in a state of the fan not turning on, that seems to be fixed, thank you for the advice!

However, it still seems like the defrost cycle warms the freezer more than I would expect, leading to significant melting of the ice in the ice tray. I have tried running the freezer with both the newer and the old mainboard, and the mainboard doesn't seem to have any impact on this. It seems like it is getting close to room temperature in the freezer during the defrost cycle. Afterwards, everything in the freezer quickly refreezes, but leaves large blocks of ice fused together in the ice shelf, that have to be removed every couple days. Is this just a normal consequence of a high-use fridge (we have 9 people living in our house, so I guess it does get opened a lot), requiring longer defrost cycles to remove all the ice? It doesn't seem like there is anything else I can replace at this point.

Anyway, thank you again for the help!

How warm the evaporator area in the freezers gets during the defrost cycle is controlled by the defrost thermistor on the evaporator coil and the main control board.