When your home's air conditioning system turns on, it initially blows out hot air for a short period before transitioning to cool air. This behavior is usually seen in heat pump systems, which are designed to provide both heating and cooling.
The reason behind this phenomenon is the defrost cycle of the heat pump. During colder weather or in heating mode, the heat pump absorbs heat from the outdoor air and transfers it inside your home to warm it up. However, when the outdoor temperature drops significantly, frost can accumulate on the outdoor unit's coils.
To prevent the build-up of ice or frost, the heat pump periodically initiates a defrost cycle. During this cycle, the system temporarily switches to cooling mode to melt the frost from the outdoor coils. This results in the system blowing out hot air for a short duration until the frost is cleared.
In your case, it's possible that the heat pump is occasionally triggering the defrost cycle even when you have the thermostat set to cool mode. This can occur if the outdoor temperature is low enough to trigger the defrost function, even if the indoor temperature has not yet reached the desired cooling setting.
If you find that the hot air blowing lasts longer than a few minutes or occurs frequently, it might be worth having a professional HVAC technician inspect your system to ensure everything is functioning correctly. They can determine if there is an issue with the defrost cycle or any other aspect of your heat pump unit.