Answer Hello Scott. You will need to check the defrost heater WR51X10042, thermostat WR50X10068, thermistor WR55X10025, and the main board WR55X10942C. Either can cause the unit not to defrost. You can test this with a multi-meter TJMA-DMT3. Here is a link on how to use a multi-meter. http://forum.appliancepartspros.com/oven-repair-including-ranges-cooktops/4810-how-check-continuity-ohmmeter.html Read More... Answered by AppliancePartsPros.com | Tuesday, November 25, 2014