The council shall choose a city manager, a city clerk, and, where required, a civil service commission, but no member of the council shall be chosen as manager or as a member of the civil service commission. Neither the council nor any of its committees or members shall dictate the appointment of any person to office or employment by the city manager or in any manner seek to prevent him or her from exercising his or her own judgment in the appointment of officers and employees in the administrative service. Except for the purpose of inquiry, the council and its members shall deal with the administrative service solely through the city manager, and neither the council nor any member thereof shall give orders to any of the subordinates of the city manager, either publicly or privately. The council, or a committee thereof, may investigate the affairs of any department or the official acts and conduct of any city officer. It shall have power to administer oaths and compel the attendance of witnesses and the production of books and papers and may punish for contempt any person failing to obey its subpoena or refusing to testify. No person shall be excused from testifying, but his or her testimony shall not be used against him or her in any criminal proceeding other than for perjury.