Proper Operation
Learn how your appliance is supposed to operate so you can determine if it is malfunctioning.

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Defrosting the Evaporator Coils

When you open the refrigerator or freezer door, all of the cold air rolls out and is replaced by air with moisture in it. If it is hot and humid in the summer you can see the cold air condense the moist air as it goes into the refrigerator. As soon as you close the door the moist air is drawn across the evaporator coils and freezes in the form of white frost on the coils. The frost will build up over a period of two or three days and would completely fill the back of the freezer section with frost. The evaporator fan could no longer carry the freezing cold air away to other parts of the refrigerator and temperatures would start to rise. The defrost system in a self-defrost refrigerator keeps this frost cleared out.

One of the key components of the defrost system is the defrost timer. The GE refrigerator timer is located down behind the toe plate and in front of the condensor coils. The timer has a switch to remove power from the compressor and divert it to the defrost heater. The switch lever is riding on a cam driven by a synchronous timer motor. The timer motor is designed to switch into the defrost mode every 8 hours. Sometimes the timer is wired to switch to defrost after 8 hours of compressor run time.

The defrost heater is positioned inside the evaporator coils. The heater coils are enclosed inside a glass tube. When the heater is on you can hear the melting frost hiss when it hits the hot heater elements.

GE Evaporator Coils
Condensate

If the defrost heater element were allowed to operate during the entire 15 to 20-minute defrost cycle, it would melt the frost and thaw half of the food in the freezer section! A defrost thermostat is wired in series with the heater element to limit the temperature in the evaporator coil section to less than 55 degrees F during the defrost cycle. The heater is on most of the time at the start of the cycle and when the frost is melted the heater is off most of the time until the cycle is over. There is a thin layer of insulation between the evaporator section and the freezer section. The temperature on the floor of the freezer can rise during the defrost cycle. Food in plastic wrapping with air spaces can start to thaw allowing the moisture in the food to evaporate into the air space. When the defrost cycle is over and the compressor comes back on, the moisture will condense on the inside of the plastic wrapper and freeze. After dozens of defrost cycles, the moisture will be drawn out of the food and deposited on the inside of the food container. This is called "freezer burn". Fish and other seafood is best when it is frozen in water. Food stored in containers with air spaces is best stored for long periods of time in a manual-defrost freezer.

When a component of the defrost system malfunctions, frost will completely fill the evaporator coil section. Water droplets will form under the evaporator section or on the top of the refrigerator section. The condensate pan down underneath the refrigerator will be dry. The icemaker, if you have one, will stop making ice and the ice in the bottom of the bin will start to melt.