The Manager may designate, by letter filed with the Clerk of Council, any qualified administrative director or department head of the City to perform his duties during his temporary absence or disability for a period not exceeding thirty (30) days. In the event that such a designation has not been made or in the event that a temporary absence or disability exceeds thirty (30) days, Council may, by resolution, appoint a qualified administrative director or department head of the City or other qualified person to perform the duties of the Manager until he shall return or his disability cease. In the event of a vacancy in the office of City Manager, Council shall designate a person as Acting Manager, who shall exercise all duties, powers, and functions of the Manager until a Manager is appointed.