Freezer Coils ReFreeze Every 2 Weeks

Our freezer coils completely freeze over like clockwork, every 2 weeks. If the ice is defrosted, the whole system works just fine for another 2 weeks. Thus far, we have replaced the control board (x2), the defrost heater, and the defrost thermostat. I’m not sure what to do next. Some research indicates a "defrost timer" might also be a problem. I was unable to find that item for my model of Fridge/Freezer, so I’m not sure if that’s actually a possible issue for us or not. Anybody have any thoughts on where to go from here?

Thanks!

Could be a temperature sensor, or a blocked vent/ grill as well. Check to see if the damper/ diffuser is opening to the fridge.