2001 E450 SD Vacuum check valve??

Ok..Hope some people get in on this since I think I'm finally close to fixing this problem. So I found the main red vacuum line off the manifold and found the line on the passenger side where it comes in the firewall. If I take the red line off manifold and run it across right to the line that comes in from firewall and connect them am I bypassing anything I can't see?? Like a canister etch and if so will it hurt anything? Again still have ac and heat coming at dash fine at idle and normal driving if I stress motor like up hill ac or heat will default to defrost then come back to dash after stress is gone. Thanks