vacuum control line to vacuum pump under pass. side glove box

I have a ford 2010 E350 triton small RV.  Climate control defaulted to
defrost because rat chewed black vacuum line going to v. pump under
glove box.  The line starts off red from interior control then goes to engine
compartment where there is a junction where the line turns black.  The
black part is chewed and then goes either directly through firewall into area
under glove box or it goes into (what looks like the fan motor box) and then
through the firewall.  I am pretty sure all I need is to replace the black line
because it is chewed after it transitions to black and before it goes back
through firewall.  My question is where does the black line go when it goes
through firewall under glove box...directly to engine compartment where I
could feed a wire into engine compartment or  does it go into the fan motor
housing.  I hope it goes directly into engine compartment because I think I
can just fish a wire through and pull it into engine compartment for a much
easier fix than dis assembling a bunch of stuff.