A residential heat pump typically takes between five and fifteen minutes to complete a full defrost cycle from start to finish. When the defrost control board initiates the cycle due to ice buildup on the outdoor coil, it reverses the refrigeration cycle and turns off the outdoor fan, causing the system to melt the ice rapidly. Most modern defrost boards are programmed with a maximum safety time limit of ten to fourteen minutes to prevent the system from spending excessive time in cooling mode during cold weather. Once the outdoor coil temperature sensor registers that the ice has melted and the coil has warmed up sufficiently, the board terminates the cycle early. You can verify that the defrost cycle has finished successfully when the outdoor fan starts spinning again, steam stops rising from the unit, and warm air begins flowing from your indoor supply vents.
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