Model #RC223AV, this side by side refrigerator was not cooling very well for the customer, but the freezer seemed to be running just fine for a while. They attempted to counter the rising temperatures by turning the fresh food temperature control to ever cooler settings, but eventually ran out of numbers on the dial. Then the freezer section started to get warmer as well preventing ice from being made and causing the ice cream to melt. While frantically looking for a possible cause, the customer found the rear panel of the freezer covered in a layer of frost which seemed weird since everything else was melting. After throwing most of the food out due to spoilage, a service call was placed to get things cool again.
Frost free refrigeration products all follow a pretty basic series of steps to ensure they remain cooling, by periodically turning off the sealed system to begin a defrost cycle. Unlike manual defrost products which require the user to unplug the unit and letting the cooling coils defrost, frost free units do this automatically on a daily basis. During each defrost cycle, a timer or control board will turn off the cooling system and turn on a defrost heater located under the cooling coils of the evaporator. This will melt away any frost that has accumulated on the coils that has accumulated since the previous defrost cycle.
The reason for a defrost cycle is simple enough to understand if you ever stuck a wet finger to a cold piece of metal. Each time the door is opened, the warmer and moister air from the room enters the cooler refrigerated cavity. As the air circulates inside, the moisture will attach to the evaporator coils and turn to ice. If the ice is allowed to continuously form on the coils, the air passages between the fins of the evaporator will close up restricting the flow of air. This restriction is usually first noticed in the fresh food section because it relies on the airflow from the freezer to maintain temperature. The way to prevent this from happening is to use a defrost heater of some kind to periodically melt the ice and drain the water to the pan located under the refrigerator.
Defrost systems vary by make and model, but generally speaking, they all have some for of control, heater, and safety thermostat to get the ice melted away. With ice forming on the back wall of the freezer like the one in this post, it is most likely one of these refrigerator parts causing the problem and preventing the unit from defrosting as it should. But if we are going to test these components, it’s best to do it while the unit is still iced over.
I started by removing the rear panel and found the evaporator covered in ice. At this point, I can make a few simple checks by manually starting a defrost cycle and taking some measurements with my multimeter. How this is done depends on the product being serviced, but on this unit which uses a mechanical defrost timer, simply advancing the timer until the fans turn off starts the cycle. With the timer in defrost, I will usually use my amp probe to verify the current draw to the refrigerator has increased from the load of the heating element. But you can also use a multimeter to verify voltage is present to the heater and to the defrost thermostat. If you find voltage but the heater isn’t working, then it’s simply a matter of figuring out where it is missing. A resistance check of the heating element will verify it is still working, while a similar check of the defrost thermostat will do the same. While the heater should have some resistance (remembering it’s an electrical load) the thermostat will either read as a short or an open. Because the thermostat is designed to be closed when it’s cold, and open when it is warm, being still in the block of ice is a good time to see if it’s working. A reading of an open circuit when cold is a sure indication that it has failed.
On this refrigerator, the defrost thermostat was reading as a short circuit meaning it was working properly and I was also reading voltage back to the freezer section. But my measurement of the heating element (elements in this case) indicated an open circuit and a failed component. The elements used on this refrigerator use coils inside of glass tubes and can usually be visually inspected for failures. Both glass tubes showed evidence of damage from their discolored appearance, so I was sure I had found the problem.
I defrosted the evaporator coils and then removed the defrost coils and their associated wiring. I also like to get the inside of the freezer cavity as dry as possible to avoid the possibility of the moisture finding it’s way into the air passages and freezing again. After installing the new defrost heaters, and putting all the wiring back into position (being careful of the sharp fins of the evaporator), I turned everything back on and put it back together. The refrigerator started cooling and the customer was ready to go shopping. In a few hours of course.
One thing to remember, once you make any repair to the defrost section, you will not be able to test the heater because the defrost thermostat will have been warmed by you defrosting the evaporator. So don’t be shocked when it is all back together and you start a defrost cycle only to not feel the heater getting warm. Give it some time to cool down, then give it another try. Or just wait and see what happens