Can't switch heat vents. All air blowing from upper vents.

my 95 Caprice Wagon has a new issue. When I select "heat", "vent", "defrost", ect, the air always blows from the upper vents on the dash. This never used to happen before. Any suggestions on what to look at, or check on?

As a little background....over the winter I did install some Corvette Fuel Rail covers, so I "could have" messed something up under the hood....???

The heat works fine as far as temperature control, but I just can't select the vents it blows air out of.
I don't like the air blowing in my face, so I want to figure this out as soon as possible.

Thanks guys!

The vacuum line for the HVAC is disconnected. It is on the passenger side of the intake manifold. If it isn't disconnected there, it will be somewhere else (or, melted inside the wiring harness bundle that is on the back of the passenger head).

Thanks, I'll look tomorrow I bet I did break the vac line, cuz of the pressure of the dang covers.

Thanks man, that vacuum hose was pulled out. I ripped the fuel rail covers off, they just strain all the wires and hoses too much for my liking!