You can use volt ohm meter to check the defrost sensor for continuity.
Auto defrost freezer not working.
When the coils are covered by too much frost and ice airflow is restricted and the freezer won t efficiently cool food.
If the defrost timer is not advancing replace it.
All you have to do is set it to come on for 15mins then of for 30 mins.
The defrost timer is such that either the compressor or the defrost heater is on but not both at the same time.
The defrost heater assembly turns on several times throughout the day to melt away any frost that may have accumulated on the evaporator coils.
It requires the owner to manually defrost the freezer coils as frost builds up.
5 check if the defrost timer defrost heater and the thermostat are working correctly.
If the defrost heater assembly is defective the defrost system will not work and frost will continue to accumulate.
Move on to the next step if this does not resolve the defrosting issue.
Do this with all the sections of the timer till you reach the beginning of the cycle again.
If the defrost sensor trips because it s not working correctly frost builds up on the evaporator fins eventually making the refrigerator and freezer not cool well.
Replace the defrost sensor if it shows no continuity at around 0 degrees f.
If any of them fails to function the defrost system will not function.
The automatic defrost should now work if there is no other issues with the defrost system.