Ok thanks for that Tom, In this model it should not be that tough, Take the food out of the freezer, Next remove the shelf's, Once the shelf's are out take the six screws out from the lower panel at the rear of inside the freezer. Once the screws are out pull the panel out, If it is frosted use a hair dryer to thaw the frost.
Once the panel is out you will see the evaporator, below the evaporator the defrost heater, disconnect the defrost heater then check it with a ohm meter, if as I suspect it reads open it will need to be replaced.
Let me know if you need the part number tom.
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