A ventilation and air conditioning system includes: an outdoor air supply fan; an exhaust fan; and a system controller to control operations of the outdoor air supply fan and the exhaust fan. The system controller includes: a link controller; an exhaust air volume receiver; a disconnection determinator; and a disconnected state supply air controller. The link controller controls the outdoor air supply fan and the exhaust fan in a linked manner. The exhaust air volume receiver receives, from the exhaust fan, an exhaust air volume signal indicating an exhaust air volume of the exhaust fan. The disconnection determinator determines a disconnected state where the exhaust air volume receiver fails to receive the exhaust air volume signal. The disconnected state supply air controller controls the outdoor air supply fan at a predetermined air volume when the disconnected determinator determines the disconnected state.