Went to this fridge freezer about 12 months ago and defrosted evaporator. Customer has now called to report he has been defrosting it once or twice a month since ( never let them see what you do, it makes them an instant expert )Tested heater etc but all seem ok. Ice appears to be at top of evaporator and heater only goes half way up !Any info would be much appreciated,I seem to remember previous models had ntc problems ?