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Does everything work fne in cool mode?
Unit is most likely shutting down on high or low pressure switch.
If it shuts down in both we are either low on refrigerant or there is a restriction in a filter drier or something. If it works fine in cool but shuts down in heat, you have a sticking metering device such as a txv. With a heat pimp you have a metering device at indoor coil and another in outdoor unit. If it works in cool but shuts down in heat you will need to replace metering device in outdoor unit.