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This indicates an air flow problem due to heavy ice build-up.
Leave it unplugged and empty with door open for around 24-36 hours.
Then plug it back and problem should be resolved.
However, if the issue appears again see if you hear the fan working.
If not, you will have to replace fan motor.
If it works you will have to replace the temperature sensor (thermostat), the issue should be resolved.
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