Dual blend door assembly

A dual blend door for a motor vehicle climate control system allows operation of the door within an air passage with lesser effort and thus may be operated by a smaller and more efficient mechanism. The dual blend door provides a main door within which is an opening covered by a smaller inner door. Both the main door and the inner door are coaxially mounted on the same pivot shaft and pivoting of the shaft first opens the inner door, relieving the air pressure exerted upon the main door. Continued pivoting of the pivot shaft beyond a predetermined angle engages drive means comprising cooperating elements of the inner door and main door to open the main door subsequent to the opening of the inner door. In broader applications, the invention constitutes a fluid passage door assembly for controlling the flow of fluid through a passage.