Hey guys I have an issue with my 96 blazer...when the ac or heat is on vent...it blows really strong out of the center vents (see image with radio) and lightly out of the siding vents (see image with headlight switch). When I switch to the defroster it'll blow out on top of the dash fine but nothing out of the little vent on the side of the dash. Any ideas? Thanks it's a 96 chevy blazer 4.3 4x4. When I got the truck 2 years ago I replaced almost all of the rubber vacuum lines and tees.

 

The vents on the ends of the dash that are pointed towards the door glass are for defogging these windows and there is very little air flow out of these. Now the vent above the headlight switch and the vent on the passenger side should have good airflow out of them.
Air distribution is controlled by vacuum actuators within the dash. The default position is such that the windshield has air flow (defrost) and this actuator will change to the dash and floor vents depending upon what is selected.
I know the '95 model had a common failure in one of these actuators and is probably the same for the '96 model as well.
The only way to fix is to replace it. The dash has to come out to do so though. Not all that difficult, just need to make notes as to where all the bolts/screws go. And it takes two people to lift dash out and in.

Good luck.

 

ok cool thank you...might as well replace the heater core if I'm going in that deep as well as the evap core

 

Heater core I agree with, not so much with the evap core. I believe there are YouTube videos on dash removal. Again not difficult other than keeping track of where the screws/bolts come from.
The steering column needs to drop down to provide clearance.

Don't forget the screws under the dash speakers.