After replacing the heater core and A/C evap core in my 98 D, I realized I had the dreaded "air only blowing through defrost vents" problem, which also caused my cruise control to stop working. After finding a wealth of information on this forum and others, I determined that I had broken the black vacuum line that runs from the brake booster through the firewall and connects next to the heater hoses. After fixing this issue with a new piece of vacuum line, my cruise control works again, but air still only flows from defogger vents no matter the setting. After thoroughly inspecting the lines under the dash, I found a red line and a brown line that appear to also be vacuum hoses connected to a separate rubber boot/grommet. I feel like this has to be the problem, but I can't find anything that it should connect to, or a diagram that shows these lines. Any help with this problem (which I realize has been covered many times on this forum) would be much appreciated.

P.S. There also appears to be a plastic connector pointing straight down from the HVAC box on the same corner where the black vacuum hose connects that seems like it should have something connected to it. It looks similar to the plastic nipple (for lack of a better term) that pokes through the firewall and connects to the black vacuum line.

 

Where is the connector for the red and brown vacuum line? I have a 98 as well, can look. But need to know which side and what general area we're talking.

 

Its hanging down when I look under the drivers side of the dash, closer to the middle of the dash than the steering wheel. It appears to maybe be coming from somewhere along the top of the HVAC Box. Its hanging not too far from where the yellow vacuum line with the rubber boot that plugs in on the lower driver's side corner.

Lol I hope that makes sense. I'm probably going to end up taking the dash back out around Thursday or Friday of this week unless I can figure out where it goes before then without doing that. I feel like it'll be a lot easier to get an idea where it's coming from and where it goes with the dash pulled out.

 

I can't see it from the drivers side floorboard. I have the entire factory service manual though, I can look when I get home from work. I know it has the entire vacuum diagram in it for the HVAC box. If you do tear into the dash, I would just remove the front cover, pull the radio, then pull the HVAC panel and look from there. I bet you'll find it.