Under Dash Vacuum Lines 85.5+

[livewirevoodoo]

What are the under dash vacuum lines for?

With the glove box removed, I see approx. 4 small diameter vacuum lines. 2 seem to come from then engine side of the firewall (where??)

The other 2 are "local" to under the dash. One has a "Y" connector. All in pretty bad shape.

Would like to replace after the torrential rains stop. I don't see these lines depicted on the vacuum diagrams tho. Any info on these lines anyone?

Thanks in advance.

[rb101]

I think the vacuum line that goes into the firewall only run the fresh/recirculate flappers in the outside portion of the HVAC system