When a ductless mini-split heat pump is switched to the heating mode but begins blowing cold or lukewarm air into your room, it is usually experiencing a normal operational cycle or a temporary system fault. First, during initial startup in heating mode, the indoor fan remains off or blows slowly for a few minutes while the outdoor coil and refrigerant lines warm up, preventing cold drafts; if the fan runs prematurely, it feels chilly. Second, the unit may be entering a periodic defrost cycle to melt frost accumulation on the outdoor coil during freezing weather, temporarily reversing the refrigeration cycle. Third, low refrigerant levels or a stuck reversing valve can cause heating failure. You can troubleshoot error codes on the indoor display panel. You can verify normal operation when defrost cycles complete and warm air resumes.
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