Written by Ian Kelly; Updated December 06, 2018. Moisture in the air collects on cold surfaces inside the freezer, forming frost. Frost, or ice, is an effective insulator as shown by igloos designed to keep Eskimos warm during Arctic winters. This insulating ice layer impairs refrigerator performance and can be caused by several factors. These include a defective door seal that allows moist air to settle on cold freezer walls or a faulty component interrupting the built-in automatic defrost cycle. Consequently, when troubleshooting frost-free refrigerators, you need to ensure that all relevant components are in working order.
Inspect both the freezer and refrigerator door seals carefully. Close both doors and inspect all four sides of the seal to ensure that it is compressed and making full contact with the sides of the refrigerator. Open the doors and inspect the rubber surfaces carefully. If you detect any cracks or signs of wear, replace both door seals.
The evaporator fan built into the back wall of your freezer blows cold air from the freezer compartment into the fresh food section of the refrigerator via a duct attached to the back wall. This duct is designed to accept cold air from the freezer and to return slightly warm air from the fresh food compartment back into the freezer to allow it to remove the heat contained in the warmer air. The defrost thermostat controls power to both the evaporator fan and the compressor by turning them on or off in conjunction with the defrost cycle. You can tell if the fan is working by either listening to it or by holding your hand over the cold air outlet in the refrigerator section. If the fan does not work while the compressor is running, it has burned out and must be replaced.
The duct leading from the freezer compartment to the refrigerator fresh food compartment can become blocked with ice buildup. The duct also contains a movable diffuser flap that allows warmer air back into the freezer compartment. Remove the screws securing the duct and make sure that it isn’t blocked with ice and that the diffuser flap is moving freely. Then reinstall the duct, close the door and allow the refrigerator to cool down. As soon as the compressor starts, open the door, hold your hand over cold air outlet, and feel if cold air is blowing out of the duct.
Mechanical Defrost Timer
For this diagnosis to work, the freezer must be frozen down or the evaporator must be encrusted with ice. Expose the evaporator coil as follows: Unplug the refrigerator. Remove the upper and lower panels from the back wall of the freezer compartment and the refrigerator section if you have a single door refrigerator. If you have a double-door unit, remove the back panel from the freezer section. Plug the refrigerator back in. Locate the defrost timer inside the refrigerator compartment; you will see a slotted screw with a pointer. Insert a screwdriver into the slot and turn the timer screw so that the pointer is opposite the defrost mode. At this point, the refrigerator will stop working. Locate the defrost heater mounted on or behind the bottom of the evaporator coil. Wait about five minutes. If the defrost heater is working, it will glow red and start melting the ice on the evaporator coil. If it fails to heat up, either the defrost timer is broken or the heater is bad and must be replaced.
Unplug the refrigerator before carrying out this test. Locate the thermostat clipped onto a freezer coil on the top of the evaporator. Disconnect the plug or spade connectors leading from the evaporator heater to the thermostat. Set your digital or analog multitester to the lowest ohms of resistance mode; if you’re using an analog meter, turn the adjusting knob on the side of the meter until the needle points to zero. Watch the readout. Insert the red probe into one of the terminals leading from the heater and the black probe into the other terminal. If the readout shows a resistance between zero and 50 ohms, the heater is good. If the readout doesn’t move, the heater is faulty and must be replaced.
With the refrigerator unplugged, open the doors and allow the interior to warm up to 30 degrees Fahrenheit or above. Unclip the thermostat from the freezer coil on the evaporator and unplug the spade connectors. Place the thermostat in a glass of cold water containing ice cubes for two or three minutes. This will allow the bimetal contacts inside the thermostat to flex and make contact with each other. Set the multimeter to the lowest ohms of resistance mode as described previously. Touch the red probe to one of the terminals and the black probe into the other terminal while watching the readout. If the readout shows zero ohms of resistance, the thermostat has continuity and is in working order. If the readout does not change significantly, the thermostat is bad and must be replaced.
Electronic Defrost Timer
If your refrigerator is fitted with an electronic defrost timer and all of the previously described components are in working order, the timer is faulty and must be replaced. Testing a programmed electronic defrost timer requires professional expertise; however, this component is relatively inexpensive; therefore bypassing the test is usually your best choice.