I had that common problem of ice buildup in freezer (located at bottom of unit). The fridge got warm. I replaced the defrost heater and then tested it to find out the old one was good. Then I ran the diagnostic and saw that the defrost thermostat was shorted. I replaced it only to have it short out and fail withing a couple weeks. I changed the motherboard and put in a new thermostat. The day after changing the thermostat, I ran the diagnostic and saw that it has failed again. Can't figure out why the defrost thermostats keep failing all of a sudden?

The refrigerator came with instructions to run a diagnostic through the light switch and temperature selections. After installing the thermostat, it indicates a 1/0. Then after a day when I run the same diagnostic, it indicates a 1/S, which , according to the instructions indicates the defrost thermostat is shorted. I will put a meter on it today and measure the resistance using the ice water technique. Thanks for answering.

Thanks. I tested the thermostat I took out and it failed. So....I haven't checked to see if the new one is working, although my thought was it should show closed while it is in the freezer just because the temp is below freezing? The only time I thought it would open is when the heating element is operating and brings the temp up on the thermostat. So far the fridge is working and the freezer hasn't required a forced defrost. It has been a week. Thanks again for taking the time to respond.