2 months back I heard a loud thumping noise in the freezer, tracked to ice buildup around the evap coil fan. removed ice and checked the evap coils to find them iced over. Tried to manually start a defrost cycle as I found indicated in several repair blogs (pushing the fridge light switch on/off several times) but this never seemed to kick in the defrost cycle so I unplugged the entire unit.
Once the evap coil thawed, I tested continuity on the heater element and it read under 50 ohms. My fridge has the ADC board instead of the mechanical defrost timer and it is integrated in the temp control panel so I bought a new one for $130 and replaced it.
The fridge worked fine for a few weeks, but now I am seeing significant failure to stay cold in the fridge part and the freezer is not staying cold enough. I heard the thumping from the evap coil fan again and when I pulled the inside freezer panel off, there was trails of frozen water dripping from ice make down to collect and freeze next to the fan, causing a large ice chunk to form, large enough to hit the fan blades. I then found the evap coil frozen into a solid block again.
Repeated the thaw process and plugged it back in. It kicked right on and is getting cold and making ice again.

I am wondering if the defrost cycle is too short or maybe the defrost cycle is not kicking on often enough or at all?
Anyone have any ideas on what I can check? What else is involved in the defrost cycle besides the defrost timer (ADC) and the heating element?

If the defrost thermostat is deformed/bulged, replace it even if it measures OK.