I measured the continuity of the defrost heater element and the thermostat and they were both good. This only left the main control board. I ordered all three because it was only a matter of time before either the heating element or thermostat went bad. I only changed out the control board and now have the other parts on hand for an immediate fix in the future. Appliance pros were awesome. I paid just a little more for the faster shipping and got the parts the next day even though I expected 2 day minimum. The website is great. Plug in your model number and it will tell you part compatibility and search out for all compatible parts. Awesome feature. Put a couple of 2x4s under the refrigerator to elevate it and make it easier to get the control board out. I used a crowbar to lift the refrigerator to place the 2x4s. Defrost problem fixed !