So I've looked at them for a while I have two vaccum lines on the passenger side of my 99 ranger that I don't know what there for or where they go. The ends I'm looking at arnt connected to anything. Any diagrams to figure out where they go. Truck runs perfectly fine.

 

Not sure for a 99 but in mine (01) those lines adjust the air vent. When the car is in f.e. uphill and the ac/fan is on, it will blow automatically blow in defrost mode (on the windshield), no matter which position the vent switch is. These 2 vacuum lines regulates this. I can take a picture of where mines are connected when I get home if your interested.

 

are you saying the air vent vacuum lines don't effect how the engine runs? I have a hole in my air vent vacuum line to the canister and the motor stalls after 6 miles of driving, can't tell if that's causing it or not

 

No. What I meant is that on my '01, there are two vacuum lines on the passenger side that goes all the way under the dashboard. And these lines will affect the air blowing from the a/c if there is a leak. If there is a vacuum leak, the air will blow in defrost mode.

 

oh okay thanks, ac doesn't work so I have no way of testing the leak, heat blows through every vent even though it has a hole on the lines you're talking about