'02 Mercury Sable defrost air volume

[steve-o tech1]

My issue is that in defrost mode there is consideralby more air volume from the passenger side than from the driver side of the vehicle. I have installed a new cabin filter with little change. There is no visual blockage and no external air leaks but I do notice air a small amount of air coming from the passenger foot heat duct. Any ideas?? Thanks Steve This vehicle is equipped with electronic automatic temp control and has no stored codes.