Definition
A defrost cycle is the routine a heat pump runs in heating mode to melt frost from its outdoor coil. The control board briefly switches the system into cooling to warm the coil, usually stops the outdoor fan and often turns on backup heat indoors. Visible steam rising from the outdoor unit during defrost is normal.
Also called: Defrost mode
Why it matters to you.
Damp air near freezing, common on Central Kentucky winter mornings, is when outdoor coils frost fastest, so local heat pumps defrost often. Steam and a short pause in warm air are normal; a unit that stays encased in ice, especially after freezing rain or an ice storm, is not.
Practical guidance.
Let defrost finish on its own, and keep snow, ice and debris from blocking the base of the outdoor unit so meltwater can drain. If the coil stays iced over, switch the system off and call a licensed technician; never chip ice off the coil or pour hot water on it.
About this definition
Written by the Feistritzer Heating & Air Conditioning team — family owned and operated in Danville since 1976, Kentucky HVAC license M02584. Definitions inform; a whole-system diagnosis in your home decides.