Customer Questions and Answers for Defrost Timer (Refrigerator) by Whirlpool

Hello Jim, There are only three components in the defrost circuit if you don't count the wiring harness. They are the defrost heater, the defrost thermostat, and the defrost timer. The timer will remove the power from the compressor and other cooling parts of the unit and apply the power to the defrost circuit when it goes into the defrost cycle. This means that the 120Vac that was going towards the units' cooling is now being applied to the defrost heater to melt away the frost build-up that is normal on the evaporator coils. It is the defrost thermostats' job to prevent the heater from getting hot enough to thaw any food that is frozen in the freezer compartment. When the defrost thermostat reaches approximately 50°F, it opens the circuit so the voltage is no longer applied to the defrost heater. It is safer to test the components with a resistance meter with the unit unplugged from its' power supply. This way you can unplug one of the wires to prevent reading back through a neighboring circuit.The defrost thermostat should show 0O of resistance. This is a complete circuit as opposed to the "OL", (overload), which shows when there is no electrical continuity. The "OL" basically means that the meter cannot read the extremely large amount of resistance shown in the open circuit. The defrost heater, if good, will read a resistance. The amount of resistance is dependant on the particular circuit. It can range from 10O to 120O, so I just look for a reading without an initial after the readout. You can also pull the wiring diagram to get the specific resistance, but you still have to realize that since mankind is not perfect, there has to be a 10%± variance to the reading. As far as testing with a test light goes, this may tell you if voltage is present, but many problems in appliances are caused by voltage drops from shorted components. The test light doesn't tell you if the proper voltage is present and could delay the repair un-necessarily. If all of the components test good, the defrost heater should turn orange when energized if the defrost thermostat is below about 20°F. If it all tests out good, there will be an air leak at fault. This will almost always be found around the door seal, unless there is an ice through the door option on the unit. The ice door is a common source of an air leak.