I have an issue with the air blowing from the center vents no matter what selection it is on. It comes out the correct vents that are selected, just come out the center vents as well. Ex if on defrost only, it will come out the defrost and the center vents. If on the floor only, it will come out on the floor along with the center vents. Does anyone know where to start with this issue. I have checked the diaphragm behind the glove box and that is working correctly.

 

Take a look at this schematic. There are two actuators that control the air flow to the dash vents - mode actuator and slave mode actuator. Sounds like you have already checked out the slave mode actuator, which is behind the glove box. The mode actuator is under the dash, near the accelerator pedal. Looks like this (brown and yellow lines going to it):



Check to see if that's working correctly. It's not uncommon for that gray plastic pivoting piece to break.

 

+1
^^ he has shown you the right path. it could also be a vac issue. check the connections behind the glove box that are rainbowed colored. most likely a damper issue though.

 

I checked the vacuum lines to the actuator that closes the flap for the center vents. If I pull that lever out manually, it closes off the center vents. I have vacuum from the brown line if center vent is selected, and not from the yellow. If I select any other than the center vent, the yellow line has vacuum and the brown does not. Is the brown vac line supposed to push that lever out and close that door?

 

If you're getting vacuum to both lines, the actuator may be bad. I would pull it out of there (carefully) and bench test it. Those things clip onto plastic tabs...can be difficult.