The appliance sometimes shuts down on defrost for long periods and food in freezer compartment starts to defrost. When working, frost covers back wall as normal, and air circulation at the back seems adequate. Customer said they thought they had heard clicking noise, so changed relay just in case, and ran ok for couple of weeks. Connections appear alright on pcb. Is there a mod on thermistor circuit as with some other Bosch models, as it appears the thermistor is sealed in?? Motor was not overheated.