A faulty adaptive defrost control is one of the most common problem with all Maytag refrigerators.
In your situation, the first thing I would do is replace the adaptive defrost control. Also you have to defrost whatever already has been built up. Just unplug the fridge for at least 12 hours with the freezer door kept open. Otherwise it will take a few days to automatically defrost it.
- The part number for the adaptive defrost control is AP3160614