Hello,
I have that common issue of the evaporator coils frozen up solid, and both fridge and freezer going warm. I thawed it out with a hair dryer and got it running again, but the frost is developing again. In the past two years, the following was replaced: motherboard, defrost element and defrost thermostat.


This time around, I've done the following:
-Confirmed evaporator and condenser fans are running.
-Ensured the condensor coils were clean. I vacuumed them out about 2 months before the problem started so they were good, but I've cleaned them again.
-Checked continuity in the defrost element, confirmed full continuity.
-Checked continuity of defrost thermostat, had continuity after sensor was placed in ice water and no continuinty at room temp. I assumed this was ok.

After I removed the defrost thermostat for testing, I connected to two thermostat wires at the fridge to try to "hot wire" the defroster element to get it going, but the element would not come on. Based on my readings online, I'm looking next to test the thermistor and mother board based on the following test procedures:

Motherboard:
[COLOR="Red"]refrigerator manual defrost test:
With the refrigerator running, unplug it and remove the motherboard cover in the back. Locate the
power connector in the bottom, left. Pull the connector off the motherboard and put a wire jumper between the connector pins that mate with the motherboard pins labeled line and def. Plug in fridg.
If you now get defrost action in the freezer, you motherboard is probably bad. If no defrost, you have either a bad defrost heater, or defrost thermostat.[/COLOR]

Thermistor:
[COLOR="Red"]The thermistor should read 5,000 ohms at room temperature(77 dgrs) / and 36 to 48,000 ohms at (0 dgrs).[/COLOR]

I'm hoping that someone can let me know if I'm on the right track. Any help is appreciated.