My old montgomery ward refridge keeps freezing up on the coil in the back of the freezer which decreased airflow then the fridge warms up. I take the freezer side apart and defrost the coils w/ a hair dryer and start it back up and it works great for a 2-3 weeks. Now last night i left the fridge open a crack all night and it warmed up again and would only get down to 50 today. I just defrosted the coils again and it will probably work fine for a few weeks. Why are my coils freezing up. 
