Digital thermostat mounted on a concrete wall

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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.

Single source ~60 min moderateBrands: Whirlpool, Maytag, Amana, Frigidaire, GE, Kenmore

Before you start

Unplug the unit before removing panels or touching the board.
Live voltage checks at the board or heater are caution work: insulated probes, one hand.
Never leave a bimetal bypassed or a test jumper in place.
Sealed-system faults are blocked: refer to an EPA 608-certified technician.

Diagnostic steps

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OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

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