Customer Questions and Answers for Defrost Thermostat (Bi-Metal) by Whirlpool

Hello Mike, There are only three components in the defrost circuit not counting the wiring harness. On this model, I would say you probably have either a bad defrost heater or a bad defrost thermostat. The defrost timer is the other component. You can use the defrost timer to assist you in the diagnosis. If you look straight up at the control box, (ceiling of the fresh food compartment), yo should see a hole that has a large plastic screw looking device in it. If you use a small screwdriver in this hole and turn it clockwise, you will hear it clicking as you turn it. It will then make a loud click. If you stop at this point, you have forced the unit into defrost. This will put voltage to the defrost thermostat. Testing at the defrost thermostat, you should read 120Vac on both sides of the device. If not, the defrost thermostat is at fault. If so, the defrost heater is open. If there is no voltage on either side of the defrost thermostat, the points in the defrost timer are at fault. Once you have found the device at fault, you can go ahead and defrost the unit with a hair dryer. This will cause the unit to cool properly for about 5 to 7 days normally while you wait on the part. When you receive the part and put it in, you will need to defrost the unit again because the defrost cycle can only melt away the amount of frost build-up between normal defrost cycles. Not defrosting the unit will cause an air circulation deficiency that you will most likely notice in you milk, (milk will spoil quicker than normal without the unit cooling at full efficiency).