When a heat pump blows cold air while set to heating mode, it is usually experiencing one of several common operational behaviors, such as being in a defrost cycle or suffering from a reversing valve malfunction. When ice accumulates on your outdoor condensing unit during cold winter weather, the heat pump automatically switches temporarily into a defrost mode—which mimics cooling mode—to melt the frost off the coils, causing the indoor fan to blow cooler air for a few minutes. Another frequent cause is a stuck reversing valve that fails to shift the refrigerant flow from cooling to heating mode. Additionally, low refrigerant levels or a malfunctioning thermostat configuration can prevent proper heating. You can verify whether the system is simply in a defrost cycle by checking the outdoor unit for steam and waiting ten to fifteen minutes to see if warm air returns automatically.
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