93 lesabre heater fan problem

I have a 1993 lesabre limited with the auto digital climate control. What i am having problems with is that even at high there is only a small amount of air flow coming out of the vents. I checked the fan and that is working correctly. I also checked all damper motors and the are all working correctly also. To me it seems like there is a restriction somewhere before the heating and cooling coils. is there anything that is located before the coils that could cause this. I just about have the dash off so i am getting cloer to the coils and hope i find something there. Any ideas would be great. Thaks