Wayne N Fountain , CO June 22, 2020 Appliance: Kenmore Refrigerator 3639554710 Kenmore Refrigerator 3639554710: Freezer was cooling fine, the fridge section of my side by side was only holding 54 deg. I found that the cooling coils were completely iced over, the defrost heaters had quit working. How to replace Refrigerator Defrost Timer. I ordered a new set of defrost heaters and a defrost timer (as a spare) from AppliancePartsPros.com and the parts arrived quickly. I removed the back panel, manually defrosted the cooling coils with a hair dryer and installed the new heater assembly. The fridge section as well as the freezer are both holding temp well now. 0 degree freezer, 38 degree fridge. The hardest part of the whole repair was taking everything out of the freezer to get to the back panel. I'm lucky enough to have a free standing freezer to put the frozen foods in while I was repairing the fridge. 1 People found this story helpful Do-It-Yourself Rating: Repair Time Estimate: 30-60 minutes