Heater & Defrost low air volume output

[1990HOTRODLINCOLN]

I am only having partial or low airflow through the Heater or Defrost vents when selected while at the same time I notice a small amount of airflow also coming through the cabin vents at the same time.It seems like the fan is not blowing with the Full force I am use to so the airflow through the heater,defrost,vent is greatly reduced.I can hear the vacuum system actuator behind the dash change to the option selected i.e. Heater, Defrost, but I cannot get full Air Volume to come through even when I select the high setting on the fan control.It seems like the fan is running on full but the air flow is not getting to the selection Heater,Defrost.

It seems to have improved very slightly as the airflow through the 4 cabin vents is now reduced when the Heater or Defrost settings are selected,then again the fan may not be running or blowing fully & I notice the drop in air volume through the vents when the Heater or Defrost cycle is selected.

The 1990 I have does not have electronic controls in the head unit but the old lever style to select the temp & cycles.
Hope this helps in Diagnosis.
Frozen in Toronto -35C Today