While one convenient function of your refrigerator’s freezer compartment is to create a steady supply of ice, either by an automatic icemaker or the old “water-in-the-molded-plastic-tray” approach, you don’t want to see a steady supply of ice building up on the evaporator coils or over the defrost drain. If the defrost drain in the freezer keeps freezing over, you may be able to fix the problem with one simple, inexpensive part: a defrost heater drain strap AKA heat probe. But more on that later.
Why is there ice building-up in the freezer anyway?
As part of the refrigeration system to keep the refrigerator compartment at a consistently cool temperature of around 40° Fahrenheit (4° Celsius) and the freezer compartment temperature near 0° Fahrenheit (-18° Celsius), the appliance’s compressor pumps refrigerant in liquid form into a set of evaporator coils (usually located behind a rear panel in the freezer compartment). Once the liquid refrigerant enters the evaporator coils, it expands into a gas which makes the coils cold. An evaporator fan motor draws air over the cold evaporator coils which chills the air. The air is then circulated through the refrigerator and freezer compartments to keep the temperature low enough to preserve food or freeze it.
Because of this process, the evaporator coils will collect frost as the air drawn by the fan motor passes over them. If the coils aren’t defrosted periodically, ice can start building up on the coils which will significantly reduce air flow and prevent both the refrigerator and freezer compartments from cooling properly. While older model refrigerators required the evaporator coils to be defrosted manually, virtually all modern refrigerators use an automatic defrost system to accomplish this. The basic components in this system include a defrost heater, a defrost thermostat, and a defrost control. Depending on the model, the control may be a defrost timer or a defrost control board. A defrost timer turns the heater on for a duration of about 25 minutes two or three times a day to prevent the evaporator coils from frosting over. A defrost control board will also turn the heater on but will regulate it more efficiently. The defrost thermostat plays its part by monitoring the temperature of the coils; when the temperature drops to a set level, the contacts in the thermostat close and allow voltage to power the heater.
So, first things first. Are the evaporator coils in your refrigerator showing signs of significant frost or ice build-up? Then here are the five most probable causes:
- Burned out defrost heater – If the heater is unable to “heat up”, it won’t be much good at defrosting. You can often tell that a heater has burned out by checking to see if there is a visible break in the component or any blistering. You can also use a multimeter to test the heater for “continuity” – a continuous electrical path present in the part. If the heater tests negative for continuity, the component is definitely defective.
- Malfunctioning defrost thermostat – Since the defrost thermostat determines when the heater will receive voltage, a malfunctioning thermostat can prevent the heater from turning on. As with the heater, you can use a multimeter to test the thermostat for electrical continuity, but this will need to be done at a temperature of 15° Fahrenheit or lower for a proper reading.
- Faulty defrost timer – On models with a defrost timer, the timer could fail to advance into the defrost cycle or be able to send voltage to the heater during the cycle. Try slowly advancing the timer dial into the defrost cycle. The compressor should shut off and the heater should turn on. If the timer does not allow voltage to reach the heater, or the timer does not advance out of the defrost cycle within 30 minutes, the component should be replaced with a new one.
- Defective defrost control board – If your refrigerator uses a defrost control board to control the defrost cycle instead of a timer, the board could be defective. While the control board cannot be easily tested, you can inspect it for signs of burning or a shorted out component.
- Failed main control board – Since the refrigerator’s main control board regulates the power supply to all of the appliance’s components, a failing board may be unable to allow voltage to be sent to the defrost system. Before you replace a main control board, you should rule out the other possible causes.
How the defrost heater’s drain strap works
Even when the automatic defrost system is functioning normally, the water resulting from the frost being melted off the evaporator coils needs someplace to go. This is why there is a drain trough located directly below the evaporator. The defrost heater heats up, the frost on the evaporator coils liquefies, and the water drips off the coils into the trough. The water then drains through a hole in the trough where it travels down a hose to a drain pan located at the base of the refrigerator. The water which collects in the pan will eventually evaporate. The pan is usually easily accessible for cleaning; just remove the appliance’s lower rear access panel to reach it.
Now here’s a problem that can occur: the freezer compartment temperature is ideal for making ice, so if the water dripping off the evaporator coils begins to freeze again before making its way through the defrost drain, the drain hole can freeze over – in other words, ice build-up will block the drain hole. This is where a drain strap can be a big help. The strap, made of copper or aluminum, can be attached directly to Calrod® – style defrost heater elements where the strap can extend into the drain hole. When the defrost heater turns on, heat is conducted through the strap to melt any ice that may have accumulated in the drain.
If your freezer’s defrost drain keeps freezing over, the drain strap may have fallen off or deteriorated. It’s also possible your refrigerator model didn’t come with a drain strap to begin with. Provided the defrost heater in your refrigerator is a Calrod® – style element, you can solve this problem by installing a new drain strap. The top portion of the strap wraps around the heater element and is usually secured with a screw. The strap should be positioned directly above the drain hole so the bottom portion of the strap can be partially inserted into the drain hole.
Solve the unwanted ice build-up problem with parts from Repair Clinic
To summarize, if your refrigerator’s evaporator coils are showing signs of ice build-up, you will likely need to replace a defrost system component to resolve the issue; if the coils show no sign of excessive frost or ice build-up, but the drain below the coils keeps freezing over, replacing the drain strap, or adding one, can fix the problem. Repair Clinic.com can help with both issues. The first step is to enter the full model number of the refrigerator in the Repair Clinic website search bar. You can then use the “Part Category” and “Part Title” filters to identify the specific parts that work with the model, whether you own a refrigerator manufactured by Whirlpool, GE, Kenmore, LG, Samsung, Frigidaire, or KitchenAid. While some refrigerator models have dedicated drain straps (or “heat probes” as they are sometimes called) that can be purchased, there are also universal drain straps available that can be installed on models using a Calrod® – style defrost heater element.