air conditioning and heating pressure

[Jimbo669p]

I have a 2001 7.3l Ford Limited Excursion. The air conditioning and heater blower system isn't blowing properly in front. The back seems to work properly. Over the last year, it has worked intermittently. Now it blows very lightly in all functions. I changed the blower fan/motor and electric vacuum comes on when you disconnect it from the canister in front of it. Could you give me some insight on what I need to try next?