Before changing parts! Most refrigerators have a manual defrost mode. This can be a little tricky to find, especially with digital controls. Check Google and YouTube with your make-a-model; I found a video demonstrating how to use my digital control panel to put the refrigerator into a manual defrost cycle. Once you know how to do this, it is much easier to diagnose and confirm fix. In defrost mode, the defrost element will glow bright orange, like a rotisserie oven. If you see this, the element is working, and the problem might be the temperature sensors or thermostat. Along those lines, once my control panel was in service mode, there was a handy mode to test all 5 temp sensors. Definitely easier to use this test mode than to cut/replace the sensors on a guess. I replaced my thermostat, and everything is working perfectly now.