Replaced the thermistor assembly. Unfortunately the first one I bought (from another site) had the wrong connector. The one I got from this site had the right connector, but the leads are somewhat shorter. It appears to be working, but I won't know for sure until a few months down the line when I can tell if the defrost cycle is working properly. This thermistor is used partially to determine if the coil has reached 40 degrees F meaning that ice melting is occurring and the coil and surrounding ducts are kept from blocking up with ice. Kind of annoying that I can't find a dead on replacement, but in both cases the thermistors seemed to be identical and gave similar measurements of resistance, so it should work OK.