Hi,Welcome to Just Answer, My name isXXXXX will be helping you with your appliance issue today.
the thermistor is bad, this senses the temperature. these are cheep. around $ 7.00 at the following link. http://www.repairclinic.com/PartDetail/Thermistor/1057227?modelNumber=AFD2535DES it # XXXXX on this diagram, its located in the fresh food section , thanks Bryan