The freezer on top unit was keeping everything up top nice and cold, but the customer began to notice things in the fresh food section getting a little to warm. When the temperature selectors were adjusted to a colder setting, it seemed to help for a day or two, but then started getting warmer again. Sounding like a defrost problem, I paid this refrigerator a visit with hairdryer in hand, and parts in the van. Frost free refrigerators use a defrost heater to periodically assist with the melting of frost that builds up on the fins of the evaporator located in the freezer section. Frost forms each time the doors are opened to the unit, and the warmer, moist air from outside gets inside and heads toward the cold surface of the evaporator. As the frost continues to collect, the air passages in and around the evaporator start to close up and begin to prevent air circulation by the evaporator fan from the freezer to the fresh food section. As the cycle continues, the temperature in and around the evaporator will be cold, but the fresh food section will get warmer because warm air is not being exchanged with the colder air from above. The defrost sections of most units will consist of the same components. Namely, the heater itself, the bi-metal terminator, and the timer or defrost control. Each one of these components need to work properly for the defrost cycle to properly keep the unit frost free. On this unit, the timer could be advanced to begin a defrost cycle, but there was no current flow to the heater. After checking all connections and doing a quick resistance check of the circuit, I determined the bi-metal terminator had failed open. These bi-metal devices are used to prevent an overheating situation in the freezer section should the heater remain on to long. Once the trip temperature is reached, the bi-metal will open up a set of electrical contacts thus opening the circuit. Then when the unit cools back down to it's reset temperature, the contacts will again close, closing the circuit for the next defrost cycle. Because this bi-metal didn't reset, the circuit remained open and no defrosting took place. After using my trusty hairdryer and warm water squirt bottle to defrost the evaporator, I wired a new defrost terminator in line with the heater. With all the frost removed, the cold air started circulating again, and now everything within the fresh food section stays properly chilled.
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