My fridge coil is freezing up every couple of days. I have checked the heater and it ohms out ok. I also noticed a defrost thermostat but do not know how to check it. What is the most likely problem and how do I check it ? Any help would be greatly appreciated.
Check to see if the evaporator fan is running. It should run at the same time the compressor and condenser fan run.
The adaptive defrost control may also be faulty. It (control board) is located in the control housing inside the fresh food section.
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Here is the tech sheet for that unit.
http://manuals.frigidaire.com/prodinfo_pdf/Anderson/240389616.pdf
It tells you how to force a defrost.
Since you know that the defrost heater is OK, checking the defrost thermostat is easy.
It should be 0 ohms when frozen.
It opens just above freezing.
You can simulate a frozen condition by holding it’s face onto an ice cube.
Note: If it looks bulged out or deformed replace it even if it does measure OK.
If you can force a defrost and the heater comes on then odds are that the defrost board needs replacing.
The fan is running ok. After having to defrost the fridge a few times I only once noticed it not working, I assume the compressor was not cycled to be on at that time because it has been working every other time I have seen it.
I checked the defrost thermostat and it appears to be open all the time, frozen or not. I suppose this means that at the start of every defrost cycle the false reading from the thermostat makes the controller think that it is already above freezing.
I will order a new thermostat and see what happens.
Thanks for all your help!