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HomeRepair HelpSub Zero Refrigerator RepairSub Zero Refrigerator defrost drain clogged Repair

Sub Zero Refrigerator defrost drain clogged

If your Sub Zero is showing a clogged defrost drain—water overflowing the drain trough, pooling in the bottom of the compartment, or ice building up in the drain tube—the most likely causes, in order, are a faulty evaporator fan motor, a frozen or clogged defrost drain, a missing or damaged drain strap, a defective drain heater, and, less commonly, a bad main control board. Start by checking the evaporator fan: spin the blade by hand and listen for unusual noise, and if it won’t turn freely or has no continuity, replace the fan motor. Use a turkey baster and warm water to clear a frozen drain and confirm the drain tube and trap are clear. Look for the small metal drain strap that carries heat into the tube and make sure any drain heater is positioned and working. Only after testing these parts should you consider the control board. Enter your model number on RepairClinic.com to pull up the exact replacement parts and step-by-step parts for your refrigerator.

01 - Sub Zero Refrigerator Fan Motor

If the refrigerator's defrost drain is clogged, it's possible the evaporator fan motor is not working. If the evaporator fan is not running, cold air from the evaporator can migrate to the defrost drain causing ice buildup in the drain. To determine if the evaporator fan motor is defective, try turning the fan blade by hand. If the fan blade does not turn freely, replace the fan motor. Additionally, if the motor is unusually noisy, replace it. Finally, if the motor does not run at all, use a multimeter to test the motor windings for continuity. If the windings do not have continuity, replace the evaporator fan motor.
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02 - Clogged or Freezing Defrost Drain

The defrost drain might be clogged or frozen. If the defrost drain is frozen, the water will overflow the drain trough and drip down to the bottom of the compartment. You can use a turkey baster and warm water to help clear out a frozen defrost drain and tube. You should also make sure the drain tube trap is clear by the drain pan.
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03 - Sub Zero Refrigerator Drain Strap

Some defrost drains are outfitted with a drain strap. The drain strap is a small piece of copper or aluminum that attaches to the defrost heater and extends partway into the defrost drain. When the defrost heater turns on, heat is conducted through the drain strap to melt away any ice that may have accumulated further down in the defrost drain. If the drain strap is not in place, the defrost drain may be more likely to freeze over.
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04 - Sub Zero Refrigerator Evaporator Fan Motor

If the refrigerator's defrost drain is clogged, it's possible the evaporator fan motor is not working. If the evaporator fan is not running, cold air from the evaporator can migrate to the defrost drain causing ice buildup in the drain. To determine if the evaporator fan motor is defective, try turning the fan blade by hand. If the fan blade does not turn freely, replace the fan motor. Additionally, if the motor is unusually noisy, replace it. Finally, if the motor does not run at all, use a multimeter to test the motor windings for continuity. If the windings do not have continuity, replace the evaporator fan motor.
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05 - Sub Zero Refrigerator Drain Heater

Some refrigerators are equipped with drain heaters. Drain heaters prevent the water in the drain pan from re-freezing and clogging the defrost drain. If your drain heater is defective or is not in the proper position, the defrost drain might freeze over.
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06 - Sub Zero Refrigerator Main Control Board

The main control board regulates the power supply to all of the refrigerator components, including the defrost system. If the main control board is defective, it may stop sending voltage to the defrost system which can lead to the defrost drain becoming clogged with ice. Control boards are frequently misdiagnosed—before replacing the main control, first test all of the defrost system components. If none of the defrost system components are defective, consider replacing the control board.
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Less Common

Frequently Asked Questions

What causes a defrost drain to get clogged in a Sub Zero refrigerator?
My freezer is cold but the fridge is warm, could a clogged defrost drain cause that?
How can I test the evaporator fan motor to see if it is the problem?
What is a drain strap and do I need to replace it?
How do I find and buy the correct replacement part on RepairClinic.com for my model?

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