You have an automatic defrost system failure causing ice and frost to build up on the evaporator coils. The evaporator coils are located behind the lower freezer panel. There is two (2) heating elements mounted under the evaporator coils and they most likely have burnt out and need replacing.
The defrost heater and harness assembly will cost approximately $55.00 plus the service fee and labor. The estimated cost of repair is about $200.00.
You probably could replace the defrost heaters yourself.
Thanks for your prompt answer. I'm sure that you are correct. I think I would like to try to replace the heaters myself. A couple of questions:
I wonder if you could send the image in some other format? The one "view full image" does not get any larger when I click on it.
Do I gain access to the heaters from the back or the inside of the unit?
Getting the parts might be a problem because Sears does not recognize the model number any longer. Do you know of a source for parts?