WARNING: This page is about a different car, the 2005 Nissan Quest. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Ducts - front heater & cooling unit assembly
Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 2: Ducts - Rear Heater & Cooling Unit Assembly - With Torque Specifications