Heat/AC works but only a little air comes out the vents

[JMA_2001XJ]

2001 XJ Sport.....Heat blows hot, the fan changes speeds and the doors work (meaning you can change the location of where the air comes out ie. the center dash, the floor and the defroster.) But my issue is that of the volume of air coming out of the vents is very minimal. Sometimes it blows a little better then other but still nowhere near where it should be. And sometimes it hardly comes out, regardless of the fan speed. Also occasionally and only occasionally, when I lift off the throttle I will get a high pitched whine from behind the dash. When that happens basically no air comes out the vents at all. I am guessing that it is still a vacuum issue but I was hoping that someone had this issue before and can guide me in the right direction of where to start. Thanks

 

[Tim_MN]

The default position of the vents when there is a vacuum leak, or no vacuum, is de-frost. The vacuum tubes can become brittle, and crack and the vacuum hose fittings are prone to drying out and leaking.

 

[JMA_2001XJ]

The default position of the vents when there is a vacuum leak, or no vacuum, is de-frost. The vacuum tubes can become brittle, and crack and the vacuum hose fittings are prone to drying out and leaking.

I figured as much, but is there any more advice? Like where to start? If I could get my hands on one of the smoke test machines, that would probably be the best way to pin point it. Thanks

 

[Tim_MN]

Start at the vacuum ball and physically/visually inspect everything in a logical and methodical manner. The vacuum tubes can become brittle and crack, and the vacuum hose fittings are prone to drying out and leaking.

.

 

[JMA_2001XJ]

Thank you for the diagram and start point. I will be getting a smoke test kit this weekend, so that should help.

 

[JMA_2001XJ]

So I got a chance to use a smoke machine this weekend. I hooked it up to the vacuum line coming off the intake manifold for the HVAC. Right away I found a hole in the rubber line running down the passenger side inner engine bay (the vacuum supply line in the pic on the left above) right by the battery. I cut out the hole in the line a spliced in a new piece and now everything is working as it should. Having that smoke machine made the job super easy.