Replaced defrost thermostat and defrost heater. I used a hair dryer to defrost most of the ice build-up. I should have waited a little longer to make sure all the ice was thoroughly melted because I broke the styrofoam piece while I was pulling it out - the bottom was still frozen in place. The videos were very straightforward, and really helped to have them playing while I was working on the fix. I used some heat shrink tubing on the defrost thermostat instead of the connector caps, and then wrapped them in electrical tape, just in case.