MIDDLE VENTS NOT WORKING... While Outer vents do????

I have a 97 cherokee 4wd 4.0 automative with 200K

I just got this and dont know the history. The ac works great on defrost. It does not blow out of the middle vents... It does blow out of the outer vents by the doors. It even sounds like it wants to work in the middle vents. It sounds like maybe something is blocking it.... i dunno... Is there a "flap" that needs to open or close or something? I am not sure what to do.. I was thinking it may be a vacuum leak but why would the outter ones work if it had a leak.... ANY help would be great.

Should I put the dash? If so how hard is that? I looked for instructions on that but found none for a 97-01 model

Thanks
TJ

You most likely have a vacuum leak. The "flapper" doors are vacuum operated. When they are low or have no vacuum, the default to the defrost vents.

There is a plastic bottle (vacuum reservoir) behind the front bumper, passenger side. There are also plastic vacuum lines that run under the battery. Check them for breakage. Follow the lines to the firewall.