Sound like you got yourself a defrost problem with your refrigerator.
There is a electronic control board for the defrost system in your refrigerator.
The electronic control board is one of three parts that make up the defrost system on your refrigerator.
The other two parts are the heating element and the defrost thermostat.
The heater and defrost thermostat are located inside the freezer behind the plate on the back wall were you see it frosting up.
They are easy to check with a ohm meter.
The thermostat should check closed (shorted) when it's covered in frost like it is now.
The heater should have some resistance. If it check open with the meter it is bad.
If both the heater and defrost thermostat check ok with a meter then I would go ahead and replaced the defrost control board.
I don't see very many bad heating elements on these.
Lots of times you can see that the defrost thermostat is bad because the back of it will be popped out like the one on the left side of the photo below.