HA's set_temperature service forwards an optional hvac_mode to the entity, and the entity is expected to apply it. The AC climate entity ignored it and only wrote the setpoint, so a set_temperature call carrying hvac_mode (e.g. a dashboard "turn on to Auto 24" button) set the temperature but never changed the mode or powered the unit on. Apply the mode first -- which powers the unit on when it was off -- then the setpoint.