I want to preface this post by saying:

Yes, it's possible to replace your AC VAC line with factory routing. But it's not fun.

I had just finished my smog/AC delete on my 94 GT when I noticed a broken VAC line above the firewall lip. \/

This line runs from the VAC tree, across the length of the firewall, through a foam grommet, and into the HVAC canister behind the glovebox. It is responsible for changing air direction to vents in the dash.

This is where it gets tricky.

It would appear that when ford was assembling the dash, they installed the line at the vacuum tree, then ran the it to the HVAC Canister, THEN installed the heater core on top of it, flush against the inside firewall. This means the VAC line we are after is squashed between the firewall and the heater core.

The air had been stuck on defrost since I bought the car, so I knew the line needed replaced.

I fishtaped what was left of the vacuum line to some spare electrical wire for extra length.\/
IMPORTANT: Make sure to wrap the tape very tightly, or else they may separate while squeezing through the firewall.

We will be using this extension to safely pull the VAC line from under the dash for 2 reasons

1. To prevent the broken VAC line on the motor side from falling through the firewall and ruining your "fish" route.
2. To pull the VAC line closer to the floor mats under the dash to free the line. There is a rubber grommet attached around it that needs to be cut off before we can "fish" our new vacuum line through.

Next you'll need to climb under the dash on the passenger side.

• Removing the glovebox will give you much more space to work, so you'll want to start there. (3 bolts)
• After the glovebox is removed, locate the HVAC canister behind it. Shaped sort-of like a miniature football. Remove the single retaining bolt and rotate it until you can see where our AC vacuum line plugs into the reservoir. After you pull that off, the reservoir should have one more vacuum line on it, but alot more slack to move. Let it lay on the floorboard next to you.
• Locate the VAC line under the dash and follow it with your fingers toward the firewall. About halfway down the line, you'll find this rubber grommet\/
  Lift it out of the upright "C" shaped housing, and set it to either side.

• Head back to your engine bay and inspect the AC/Heat Box Foam Grommet. If you push your finger into the grommet, along the VAC line, you'll feel a sharp left and downward turn.
• The VAC line doesn't just go through the foam grommet. After it enters the grommet halfway, the line turns 90° left and about 45° down. (through the foam just past the firewall, then parallel along the inside firewall face)
• Grab a knife and try to cut from the middle, to the bottom left, where you felt that VAC line exit that foam.\/
  Pull the VAC line down and left, along the line of the cut you just made. Here's a photo of what the entire foam grommet looks like when removed properly from behind the firewall.\/
  
  Cut through as little foam as possible to make a path for the VAC line to travel through. Here's a pic demonstrating the angle the VAC line exits the foam.\/
• Triple check your tape job in the engine bay is tight. If possible, flare both ends of the tape with taller layers in the middle: like so.\/
• Pull the slack out of the VAC line from under the dash, cut where foam is in the way, repeat. This works alot better with a friend who can keep light tension on the VAC line from under the dash, while you cut the foam to free the line. Just put tension on the wire from the backside and cut in front of where the VAC line is leading you.
• Once you cut the foam deep enough, you'll feel and see a white gasket-like rubber near the bottom. This is normal, its a gel thats built into the foam grommet.
• Try to pull all slack from the line, from behind the dash, so that the tape flare you created sits pointing downwards toward the hole. When the grommet is cut deep enough, the person under the dash should be able to see the tape start to push through. Have a friend push the tape flare straight into the hole, whilst you pull from underneath. Pull your fish line through! This will give you much more room to cut the grommet off the VAC line.
• Next, you have to cut the VAC line rubber grommet off. This will free the VAC line to be pulled through the firewall from the motor side. Take a fresh razor blade and cut perpendicular to the VAC line.\/

Important: Be careful not to cut the VAC line itself while doing this, any damage to the wire could increase your chance of snapping it while pulling.

• After removing the grommet, grab your replacement vacuum line and link the ends together under the dash. I pulled a spare VAC line out of a parts car, and happened to have a few vacuum fittings around to connect them. Tape this tightly!\/
  
  
• You'll need to un-do the room you just gave yourself, and pull the "fish" line back into the engine bay, exposing the end of the VAC line we first taped the electrical wire to.
• You should notice you have FAR more VAC line coming out of the grommet before it bottoms out, this is because we got that grommet out of the way.
• Have a friend pull the line from the engine bay, while you push hard from underneath in the direction of that hole et voila. You now should have your new vacuum line in!
• Remember to place the rubber grommet back in the upright "C" shaped housing (OEM replacements with grommet only), and plug your new VAC line into the HVAC Canister.
• Reinstall HVAC Canister and Re-Mount your glovebox door.
• Reattach your new VAC line to the vacuum tree, and you're done!

I hope this guide helps anybody else that has ran into this problem. Here is a link to another thread I found on this issue:

Routing HVAC vacuum line through firewall

~ I already had my AC system deleted so that helped quite alot. You may need to remove the condensation tank for better access. I was able to repeat this repair on an AC car, so it is possible.

Looking forward to any input or replies, I'll check this thread occassionally to answer questions! Please Bump!

VACUUM DIAGRAM: