this line was cut off when I got this truck. It comes out by the firewall. And where can I get one? thanks

 

That is a splice block for the HVAC vacuum lines. If you want to repair it, you can slip a regular small black rubber line over the hard plastic one.

Does the white line go to a actuator by the hood hinge on the pass side? Does any of your HVAC controls work in the dash when the engine is running? Will it go from defrost to vent, to floor? If not, that black line may be the main vacuum supply line.

 

Here is where the HVAC main line hooks in. It's on the vacuum tree on the firewall.

 

This shows where the black line goes, upper left corner of the diagram below.

 

 

Yes 1 line is the supply and the other goes to the vacuum motor in the engine bay by the hood hinge.

I had the supply line go bad in the rubber that the lines are in.
Had vacuum in the engine bay side but nothing inside to the HVAC control
Took me a bit to figure that out and even longer to get a hose thru the rubber.
Dave ----

 

thanks, I don't know what the vacuum motor is or looks like.

 

Look in the engine bay on the top of the HVAC box you should see that vacuum hose going to a part, that would be the vacuum motor.
When the HVAC controls are moved vacuum is sent to that part / vacuum motor and it pulls on the lever that moves a flap / door inside the box.
Here you are looking at the box (removed) from the inside / under dash.

The one you would see in the engine bay is on the right just above the opening.
There are 2 more to the left, the silver things, that are under the dash.
Dave ----

 

You just took a picture of it in post #5. That actuator controls your inside/outside air. All functions are outside air except "MAX A/C" which will then move the actuator over near the hood hinge in the picture above, and let it draw inside air in the system.