AC Blower not cutting it

[Zip7SC]

Own a 1986 GMC Sierra K1500.  Factory AC has been upgraded.  Freon is fully pressurized.   Air blows relatively cold, but barely comes out of dash-mounted vents (the floor vent works ok).   Is this a common problem?   Will upgrading the blower/fan provide a boost?   Is there a quick fix to this problem or should I have a professional diagnose?    Great forum.  Appreciate any and all feedback.   90+ degrees here in SC until Labor Day!    Thanks.

[roundedline]

Sounds like your flaps may be closed if it is blowing down to the floor harder than above.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project

[Zip7SC]

Roundedline,
Thanks for the reply.  Now to followup a dumb question with an even dumber one.....is there a single flap that inhibits (and allows airflow) to all the vents, and where would that be?   I'd look rather than bothering you, but I'm at work and the truck is home.     I appreciate all you add to this site.   I find it very helpful.
Thanks.

[VileZambonie]

Check the vacuum hoses at your reserve cannister in the engine compartment.