A heat pump blowing cold air while operating in heating mode is typically experiencing a normal defrost cycle, a stuck reversing valve, or a low refrigerant charge. During winter, outdoor coils can collect frost; to melt this ice, the heat pump reverses its refrigeration cycle temporarily into defrost mode, which blows cool air indoors for a brief period. However, if the system continues blowing cold air indefinitely, it often indicates that the reversing valve is stuck in the cooling position, preventing hot refrigerant from flowing to your indoor coil. Other potential culprits include a faulty thermostat setting or a severe refrigerant leak. You can verify the defrost cycle hypothesis by checking if the outdoor fan is stopped and steam is rising from the outdoor unit, after which normal warm airflow should resume within ten to fifteen minutes.
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