Sub-Zero · Refrigerator error code

15 4 01Defrost relay stuck closed

Cross-checked High-voltage / caution

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Related diagnostic guides

Component test · Refrigerator

How to test a refrigerator bi-metal defrost thermostat

The bi-metal (defrost termination thermostat) is wired in series with the defrost heater. It is closed only when the evaporator is cold and opens once the coil warms during defrost. Testing it at room temperature gives a false "bad" result: it must be cold.

5 steps ~45 minmoderate

Guide · Refrigerator

Adaptive defrost control (ADC) board: how to diagnose it

An adaptive defrost board replaces the old cam timer. It counts compressor run time (and on some boards door-open time) and adjusts the next defrost interval based on how long the last one took. Test the heater and the cold bimetal first, then force a defrost: if the heater warms on a forced defrost but the coil still ices, the board isn't starting defrost on its own.

8 steps ~60 minmoderate

Guide · Refrigerator

Known issue: Whirlpool / Maytag / KitchenAid three-door French-door 'frost clog' (fresh food warm, freezer OK)

A class settlement (Paperno v. Whirlpool, N.D. Cal., final approval May 13, 2025) covered certain Whirlpool, Maytag and KitchenAid three-door French-door refrigerators built roughly 2012 to 2019 that may not fully defrost the fresh-food evaporator, so frost and ice block airflow and the fresh-food section stops cooling. Whirlpool denied wrongdoing. The settlement reimbursed documented evaporator repair or replacement costs within limits; reported claim deadlines were in 2025, so new claims are likely closed. The repeat-icing pattern is still common in the field.

8 steps ~90 minadvanced

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