I have a Frigidaire side by side refrigerator (Model FRS26ZGE) that the coils in the freezer continue to freeze up and the refrigerator gets between 60-70 degrees. 6 months ago a repairman replaced the defrost timer and it worked fine for a short period. Now, about once a week I have to unplug and manually defrost the freezer. Is there some other problem going on?