HVAC vents

I noticed on my 90' B2600i that the defroster vents on the top part of my dash aren't blowing at all... no matter what setting I put it to. This is really causing some bad problems with my windshield fogging in the colder mornings or when it's raining.
Is there something that I can do to fix this? Seems like the only air blowing out is through the dash vents. I don't have any lower vents blowing on my feet either.

may have a pull line bent or poped off check that out, they are on the drive side of center of the box under the dash

Do I have to pull the whole dash to access them?

No. Just take a look under the dash just to the right above the gas pedal. And you will see the side of the black box the has to two cables going to it make sure they are still connected.

Cool thanks guys. I'll check that out later today and report back.

You guys are awesome! One of the cables popped off. All fixed now! Thanks so much!

no prob man