Kenmore Elite 596.77603801 Fridge works but freezer temp fluctuates

Kenmore Elite 596.77603801 Fridge works but freezer temp fluctuates The fridge in my 12 year old Kenmore Elite works fine, but the freezer temperature fluctuates by 10 to 20 degrees at least once a day. The freezer still makes and dispenses ice, but food is thawing and refreezing every day. How do I diagnose what the problem is?