96 Blazer Possible Vacuum Leak?

I was replacing the heater core and I have noticed prior to doing this that I could hear what sounded like a vacuum leak under the dash. Since I had the entire dash taken apart I decided to start the vehicle in order to locate where the noise was coming from. To the best of my knowledge it is coming from directly behind the controls. If I turn the control to floor and dash the noise is eliminated I have taken a picture of the back of the controls. There is one tube that does not have a vacuum line running into it. I am curious if this should be the case. Also, I am looking for any additional guidance or advice on how to determine whether or not everything is operating properly.

https://www.dropbox.com/s/w2nxfdx8bl84zc7/2013-01-03%2011.37.56.jpg

https://www.dropbox.com/s/w2nxfdx8bl84zc7/2013-01-03%2011.37.56.jpg

I have attempted to insert the picture directly and included a link to the photo if that does not work.

I was replacing the heater core and I have noticed prior to doing this that I could hear what sounded like a vacuum leak under the dash. Since I had the entire dash taken apart I decided to start the vehicle in order to locate where the noise was coming from. To the best of my knowledge it is coming from directly behind the controls. If I turn the control to floor and dash the noise is eliminated I have taken a picture of the back of the controls. There is one tube that does not have a vacuum line running into it. I am curious if this should be the case. Also, I am looking for any additional guidance or advice on how to determine whether or not everything is operating properly.

https://www.dropbox.com/s/w2nxfdx8bl84zc7/2013-01-03%2011.37.56.jpg

https://www.dropbox.com/s/w2nxfdx8bl84zc7/2013-01-03%2011.37.56.jpg

I have attempted to insert the picture directly and included a link to the photo if that does not work.

The control uses only 5 vacumn lines.
The other port is a vent.
Should not leak vacumn after it vents after switching control positions.

The control uses only 5 vacumn lines.
The other port is a vent.
Should not leak vacumn after it vents after switching control positions.

Thanks. So if I understand this correctly, after I turn the control from off to anyone of the a/c or heater controls it should not continue to leak?

Before I get ahead of my self would testing the vacuum at the test port under the hood could I detect if there in fact is a leak?

Thanks. So if I understand this correctly, after I turn the control from off to anyone of the a/c or heater controls it should not continue to leak?

Before I get ahead of my self would testing the vacuum at the test port under the hood could I detect if there in fact is a leak?

Should not keep on leaking.
It is only a vent to release vacum pressure to the actuators.

No on under hood port.

https://www.dropbox.com/s/l9nvoyyja2ywu4p/2013-01-09%2013.21.00.mov

I have attached a video where you can hear the vacuum in the background. There are two settings in which the vacuum doesn't leak.

https://www.dropbox.com/s/l9nvoyyja2ywu4p/2013-01-09%2013.21.00.mov

I have attached a video where you can hear the vacuum in the background. There are two settings in which the vacuum doesn't leak.

the sound is to me a wirling sound. use a vacuum gage to see if the switch or vent damper is leaking or hoses/fittings. with a gage and pinching hoses this should be fast locating.

video is not all that good for me to observe with my computer. 68 meg file and very short with a odd sized screen format.