def set(self, mode):
        """Set the thermostat mode.

        Mode optons:
            OFF = 0x00,
            HEAT = 0x01,
            COOL = 0x02,
            AUTO = 0x03,
            FAN_AUTO = 0x04,
            FAN_ALWAYS_ON = 0x8
        """
        if mode == ThermostatMode.FAN_AUTO:
            new_mode = COMMAND_THERMOSTAT_CONTROL_OFF_FAN_0X6B_0X08
        elif mode == ThermostatMode.FAN_ALWAYS_ON:
            new_mode = COMMAND_THERMOSTAT_CONTROL_ON_FAN_0X6B_0X07
        if new_mode:
            msg = ExtendedSend(address=self._address,
                               commandtuple=new_mode,
                               userdata=Userdata())
            msg.set_checksum()
            self._send_method(msg, self._mode_change_ack)