2005 Mercury Mariner vacuum line pass-thru
 

There's no Mercury forum I can find so hopefully the Escape crowd can help me. :)

I have a 2005 Mariner V6. I just replaced my alternator using the 'pull-up' method from behind the motor. And during the process I unhooked a vacuum line that comes out of the oblong vacuum canister that hangs on the firewall...just behind the intake manifold. I can't find where to reconnect it and can't find a diagram anywhere. I 'think' it might pass through the firewall somehow and connect to the vent actuator underdash. But I can't find a hole anywhere for it to pass though.

Anyone vacuum line gurus familiar with this line?

Sorry no guru here !
Usually, the vacuum path originates at the intake manifold, goes to the reservoir and from there goes to the inside of the vehicle.
Have you checked to make sure that line does not come from the intake manifold area?
If you start the engine there should be vacuum present on that line, if not, it goes to the manifold or a multiple vacuum connection near the firewall.

Solution
 

Figured it out. This tiny vacuum hose passes through a small hole in the firewall between the two AC hoses. It snakes through a rubber grommet and connects to a black hose that operates the vents. Seems like this one little hose is responsible for the whole vent system. My symptoms were that AC only came out of the defrosters, no heat.

I used a hook to pull out the grommet under dash, and used a stiff plastic hose to pass to the inside. I taped the vacuum hose to it and pulled it into the glove compartment to reconnect. AC and vents work perfectly now. Obscure cause to what seems like a common problem. on the Escapes/Mariners/Tributes.