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Differences Between Adaptive Defrost Control and Defrost Timer

Pamela Gardapee

Freezer and refrigerators have defrost timers or adaptive defrost functions that will keep the freezer and refrigerator compartments free of frost. The main difference between the two types of defrost functions is how each one keeps the units free of frost, which you should known before purchasing any freezer unit.

Adaptive Defrost Control

Refrigerators or freezers that have adaptive defrost controls will defrost only when the unit needs it. This feature uses electronic controls to determine when the refrigerator or freezer needs to be defrosted. The control board monitors how many times and how long the doors are opened, how long the compressor has been running since the last defrosting cycle and how long the heater for defrosting was on the previous time.

Adaptive Defrost Control Operation

When the defrost mode turns on can vary, from every eight to 100 hours. The first time a refrigerator or freezer with an adaptive defrost function starts up, the defrost cycle will kick in after the unit has been running for eight hours then again whenever the unit needs it. The purpose of this is so the control can continually adapt to when the unit needs to be defrosted for optimal performance.

Defrost Timer

The defrost timer controls the refrigerator or freezer's defrost cycle. Defrosters run as a clock that continually starts the defrosting process for 12 to 32 minutes then returns the unit operation to cool. After so many hours of run time, the defrost timer signals the heat circuit to open and the compressor circuit to close. At this time, the refrigerator or freezer is in defrost mode. After the defrost cycle is over, the timer signals the heat circuit to close and the compressor circuit to open and continue cooling the unit.


Adaptive defrosters have five cycles: cooling, pre-chill, defrost heater, dwell period and post dwell period. The defrost timer has three cycles: cooling, heating and dwell period. The dwell operation is the time between when the heating operation stops and the condenser starts back up to cool the unit. There is a delay to the compressor start up so that any remaining melted water can drip out of the unit before the cooling cycle causes it to freeze again.