Forcing a residential heat pump into a defrost cycle is a diagnostic procedure used to test whether the defrost board, sensors, and reversing valve are functioning properly when checking for ice issues. To force a defrost, the heat pump must be actively running in heating mode with a steady call for heat from the indoor thermostat. You must remove the outdoor unit's service panel and locate the defrost control board, specifically identifying the test pins usually labeled TEST or TFS. Using an insulated jumper wire or metal screwdriver tip, briefly short or bridge these two test pins together for a few seconds according to the board instructions. This action bypasses the standard time delay and forces the system into defrost mode. You can verify success when the outdoor fan stops and steam rises from the coils.
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