When a ductless mini split heat pump blows cold air while set to heating mode, it is typically experiencing a normal startup defrost cycle, oil return cycle, or a refrigerant pressure issue. Mini splits feature intelligent inverter controls that routinely pause heating or temporarily reverse the refrigerant cycle to melt frost accumulating on the outdoor condenser unit during cold weather, which causes the indoor wall cassette to blow cool air for a few minutes. Another potential cause is that the unit is still in pre-heat standby mode right after turning on, waiting for the indoor coil to warm up before engaging the indoor fan to avoid blowing chilly drafts. Additionally, low refrigerant levels from a flare fitting leak will severely impair heating capacity. You can verify whether the system is simply in a defrost or standby cycle by checking the indicator lights on the indoor unit and waiting ten to fifteen minutes to see if warm airflow resumes automatically.
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