I have an old KitchenAid KBLC36FMS00 built-in refrigerator (with freezer on the bottom). The tube drain from the evaporator tray is not heating. As a result, the condensation from the refrigerator (on top) is freezing in the tube drain, causing the evaporator tray to fill with water and freeze. This also results in condensation running down into the freezer, causing a lot of ice to build up.

I replaced the evaporator fan motor and the thermistor. Now I need to determine how to get the drain to heat properly. Given that this is an older model, I am not certain what the next step should be. I welcome any advice. I am not a professional, but am very comfortable swapping out parts and working with appliances.