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HomeRepair HelpSub Zero Refrigerator RepairSub Zero Refrigerator not defrosting Repair
Sub Zero Refrigerator not defrosting
If your Sub Zero refrigerator is not defrosting, frost and ice buildup on the evaporator coils is the symptom you see and the causes are usually straightforward. The most common reason is a door left open or not sealed, which lets moisture in and creates heavy frost that may clear after normal cycles or need the unit unplugged or warmed with a hair dryer to melt. Next to check are the defrost control board, then the defrost timer; a failed board or timer can prevent the unit from entering or powering the defrost cycle. Also inspect the door gasket for twists or gaps that stop the door from closing fully. Finally, the defrost heater assembly and the defrost thermostat can fail and leave the coils frozen solid. Before replacing the control board, test the defrost heater and thermostat for continuity. These are the usual fixes for refrigerator not defrosting or fridge not defrosting issues. Enter your model number at RepairClinic.com to find the exact replacement part for your refrigerator and the step-by-step parts and testing guides you need.
01 - Door left open
If the freezer or refrigerator door was left open for an extended period of time (more than 4 hours), frost or ice may have accumulated on the food, evaporator coil and evaporator fan motor, or around the door opening. Frost should go away after the door is closed and the refrigerator goes through a defrost cycle. More significant ice buildup may require the refrigerator to be unplugged for a day to allow the ice to melt, or a hair dryer may be able to be used to assist in melting the ice.
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02 - Sub Zero Refrigerator Defrost Timer
The defrost timer turns on the defrost heater several times throughout the day to melt any frost that may have accumulated on the evaporator coils. If the defrost timer is defective, it may not advance into the defrost cycle, or it may not send power to the defrost heater during the defrost cycle. To determine if the defrost timer is defective, slowly advance the dial into the defrost cycle. The compressor should turn off and the heater should turn on. If the timer does not send power to the defrost components or advance out of the defrost cycle within 30 minutes, this indicates that the defrost timer is not advancing. If ...
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03 - Sub Zero Refrigerator Defrost Control Board
The defrost control board determines how often to run the defrost cycle. If the board fails, the refrigerator will not go into the defrost cycle. Before replacing the defrost control board, first test the defrost heater and defrost thermostat. If the defrost heater and defrost thermostat are working properly, the defrost control board is likely defective.
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04 - Sub Zero Refrigerator Door Gasket
A twisted or worn gasket can keep the door from closing properly. Inspect the door gasket for kinks or twists. You can use a hair dryer to try smoothing out the kinks. If the door gasket is damaged it will need to be replaced.
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05 - Sub Zero Refrigerator Defrost Heater Assembly
The defrost heater assembly turns on several times throughout the day to melt away any frost that may have accumulated on the evaporator coils. If the defrost heater assembly is defective, the defrost system will not work, and frost will continue to accumulate on the evaporator coils. To determine if the defrost heater is defective, use a multimeter to test it for continuity. If the defrost heater does not have continuity, replace it.
Common
06 - Sub Zero Refrigerator Defrost Thermostat
The defrost thermostat monitors the temperature of the evaporator coils. When the coils drop below a set temperature, the thermostat contacts close to allow power to flow to the defrost heater during the defrost cycle. In the defrost cycle, the defrost heater melts away any frost that may have accumulated on the evaporator coils. If the defrost thermostat is defective, the thermostat contacts will not close. As a result, the thermostat won’t provide power to the defrost heater. To determine if the defrost thermostat is defective, use a multimeter to test it for continuity. If the defrost thermostat does not have continuity...
Common
07 - Sub Zero Refrigerator Thermistor
A thermistor monitors the temperature of the evaporator coils. If the coils are below a set temperature, the thermistor will alert the defrost control to allow power to flow to the defrost heater during the defrost cycle. In the defrost cycle, the defrost heater melts away any frost that may have accumulated on the evaporator coils. If the thermistor is defective, the defrost control will not be alerted to allow voltage to be sent to the defrost heater.
Common
Frequently Asked Questions
My Sub Zero refrigerator is not defrosting. What should I check first?
How do I test the defrost heater and defrost thermostat?
Could the defrost timer or defrost control board be causing the problem?
Can a bad door gasket cause excessive frost or prevent the refrigerator from defrosting?
How do I enter my model number or part number on RepairClinic.com to find the right replacement part?