Model #AFD2535FES, this bottom mount (freezer on bottom) refrigerator was cooling fine in the freezer section, but the fresh food section was warm enough to make the milk spoil. The customer decided to turn the unit off overnight after loosing most of the food, and found the temperature back down where it was supposed to be. But about a month later, the temperature started to creep back up in the fresh food section, so instead of loosing more food, I was called to see if I could solve the problem.
Most refrigerators in home today utilize a sealed system to provide cooling inside the unit food cavities. This system doesn’t actually cool, but rather removes heat from the items and the air that enters each time the doors are opened. Sealed systems use an evaporator located within the freezer section to remove the heat, and in conjunction with a fan to provide air movement, this is basically how everything gets cold in the freezer.
The fresh food sections usually have no independent cooling system, but rather rely on the air movement from the freezer fan along with an air damper, or diffuser to control the movement of cool air that enters the cavity. The air that enters absorbs heat as it passes through the food items and eventually returns to the freezer through one or more air returns to complete the cooling cycle. Because the entire cooling process is very dependant on the proper movement of air through both sections of the unit, any disruption or restriction will result in poor cooling usually in just one section of the refrigerator.
Now that we have the basic understanding of how the refrigerator cools, the reason for this units failure can be better understood. The frost free refrigerators utilize a defrost system to remove any frost that builds up on the evaporators cooling fins that might disrupt the air flow as it passes through the freezer section. This frost occurs due to warmer moist air entering the unit each time the doors are opened and if not periodically melted away, the evaporator fins will eventually become blocked enough to prevent the air from moving into the fresh food section. Without this air movement, the fresh food section will begin to warm, while the freezer sections will remain cool.
This was the exact scenario this customer was experiencing, and although the reason for the failure can be a few different items, I usually head straight for the most likely refrigerator part to cause this type of failure.
The defrost section of most refrigerators will comprise a heater of some type, a defrost timer or control board, and a defrost thermostat or terminator. Each of these components are needed for the defrost cycle to work properly and any one item failing can result in a blocked evaporator, so the thing I will do when dealing with a suspect defrost problem is to initiate a defrost cycle to check the system components. How this is done depends on the individual make and model of refrigerator, but it is an important step to verify you have power to the system. If you don’t it’s time to find out where the power is missing.
On this refrigerator, I had voltage present into the freezer section, but the element wasn’t heating. A resistance check of the element showed a good circuit, which left my likely part failure as being the defrost terminator. This bi-metal thermostat is designed to open the circuit at a specified temperature and then close the circuit at a lower temperature. Used as a safety device to prevent heat damage to the freezer interior, these thermostats have a rather high failure rate and are often the reason for defrost problems. Because the terminator on this refrigerator was encased in ice, I figured it should be cold enough to be a closed circuit, but a resistance check with my meter showed otherwise. The terminator was reading as an open circuit which means I found the problem.
Most replacement defrost terminators come as a kit with a pair of wire nuts allowing for simply cutting out the old part, and installing the new. With the new terminator installed, I used a steamer I keep in the van to defrost as much of the evaporator as I could so this customer would have a working refrigerator when I was done. After putting everything back together, I cleaned up the mess, the cold air was blowing into the fresh food section above, and in a few hours, this unit would be ready to keep food cool again.
By the Way, once the new terminator is installed, you will not be able to initiate a defrost cycle because the terminator has been at room temperature and thus, is an open circuit. If you give it time enough to cool past the reset temperature, then you can try the defrost again, just to be sure everything is working properly.