Refrigerator

Have looked at the schematics for this cabinet and am unsure as to the location of both defrost thermostats as unclear on drawings. The purpose of the defrost thermostat is to overide the heater and end the defrost cycle, once the temperature on the evaporator is high enough (normally around 0'C). If you have two then one will probably control the heaters going off and the other may well control the fan, for coming back on. I.E. once the defrost has ended the second sensor will tell the fan when the coil is cold enough to come on, this prevents heat being pushed into the main area after a defrost cycle. If you feel competent enough then I would bypass the heater thermostat temporarily and see if the heaters kick in. The other thing to check is that you have a resistance across the two ends of the defrost heater. In my experience the heater is the most likely to fail, the sensor sometimes fail and the timers rarely fail. The age of your cabinet would suggest the heaters. Please do not leave the sensor bypassed as it performs an essential role. Hope this helps.