I Removed the back inside panel of the freezer. Frost was all over the evaporator. The defroster heater was not working. I ordered the defrost timer and defrost heater. I bought both to be sure I didn't have more than one failure point. The frig is 18 yrs old so I figured I'd be sure i don't have this problem again. After allowing time to melt all the frost, I replaced both components. Surprisingly easy. Replaced both components in about 30 minutes.