Refrigerator is not staying cold

Hi KevinBrown-I have a few questions- how did you determine the heater was bad? When you removed the evaporator cover to have access to heater, how much ice/frost was on the coils? Was the ice/frost pattern covering the coils evenly or was frost only on the top of evap or maybe just on one side? Did you test the defrost thermostat-some call it a bi-metal? Did you test the defrost sensor? Both are located on or near the heater. These components can be tested with a multimeter that measures ohms/resistance. This must be done with refrigerator unplugged. If you've done this already , great! Please reply with your answers and the readings for each component. If all components test good then the problem is in the main control PCB. Thanks!