I have a KBFS25EWWH9 refrigerator. We noticed that the refrigerator was warm. I opened the freezer and found that the evaporator fan was still spinning. The evaporator was totally covered with ice. I tested the defrost heater and found it to have 28 ohms resistance, so OK. I tested the thermistor and it seemed to be OK---but I replaced it anyway because I had to cut off the old one to test it.

After turning the fridge back on, I can see that ice is forming again on the evaporator, so it doesn't seem like the problem is resolved.

I've been advised to examine the defrost thermostat or the defrost timer, but these parts don't seem to exist for my model. (The only thermostat is for the ice maker, and a search for timer just turns up the icemaker thermostat.) So I'm not sure how to proceed.

I was given a Tech Sheet for the fridge that seems to somewhat match my model. I ran through the various tests and couldn't clearly identify anything wrong. Once we saw the ice forming I tried a "force defrost" cycle. That didn't seem to have any effect on the ice.

What should I do next?