Trying to figure out what this is connected to the vacuum lines heading to the cruise control and hvac? As a check valve it don't work when I blow through it but I have read on here it's a filter to.

 

Its a check valve. it will blow thru 1 way and not the other.

 

Damn, I was afraid of that, I can blow and suck through it no problem. Guess the blower must have poped it over time.

 

Just letting people know you can pick up one of these check valves in the help section, everything is exactly the same as the stock one. I also ordered up a spare through GM part #15733271

 

I know this is an old thread but I wanted to add to it to help others further. Hopefully, what I learned today can help someone else.

I was looking to see if there was a diagram showing the orientation of the check valve and ran across one in my PDF manual. Figured I share the diagram with all. The check valve in question is located between items [1] Vacuum Tank, [2] Engine Vacuum Source and [3] Black Tube as seen in the diagram. Based on its purpose, when manifold vacuum pressure rises (under load) the check valve should close leaving ports [1] and [3] common while closing off [2] vacuum 'source', or the lack there of in this instance. This allows stored vacuum pressure from the Vacuum Tank to support the cruise control actuator (not shown) and A/C.

I've also added pictures showing direction of airflow as it relates to check valve position with Source Vacuum present and not.

 

Bennett, on your "check valve closed" diagram, wouldn't the (1) and (3) arrows be reversed? Without manifold vacuum, wouldn't the vacuum canister be pulling airflow in the opposite direction than you're showing?

 

The 2 "clear" or "white" connections are the same, functionally. Direction of "flow" depends merely on which one is connected to the vac reservoir and which is connected to the vac "loads" (cruise & HVAC). The same thing could be accomplished using a valve with only 2 ports, and a tee. You are correct though, as the diagram is drawn, the reservoir is connected to the one that's inline with the source and the "loads" to the one at a right angle, so those arrows would be pointing the other way under the "no source vacuum" condition.

 

I think this check valve is the "missing link" I have been trying to figure out. I have a vacuum port on my intake that is capped off:



And I have what I believe to be the HVAC vacuum tube here:



I also have a hose from the charcoal cannister and cruise control thing that almost reaches the vacuum port on the intake.
The two loose hoses are 5/32" , but the intake port is bigger. Maybe not 3/8", but close. Maybe 5/16". The check valve shown above looks to have one port that is slightly bigger. Is this what I am missing here?
All of my engine vacuum hoses are intact, so I am thinking these must go together. The diagram above makes me think this, but I'm not certain.

 

Check this out, this is how I have my check valve hooked up and my vents work properly.

 

Awesome. I think that answers my question. I have a check valve coming today.
To anyone who may have this problem, the reviews for the Dorman part say it does not work. It's basically a tee not a check valve. I did find a GM one at Oreilly for about $6, which was cheaper than the Help! version.