Nice day today so I decided to change some dried out vac lines on my 96 blazer w engine. In changing the vac hoses from the vac ball on the hood I removed and dropped the "T" valve without first observing which way it goes. Since I couldn't find it I went to auto zone for a replacement. Of course when I returned I found the old T in the engine bay.Now my problem. I can blow thru the new T valve in both direction and feel air coming out thru either end.
Now with the T that was originally in the vac lines,If I blow thru the smaller end I can feel air out the other end.If I try to blow air thru the larger end (its black) air will not pass thru. Are these T valves supposed to have air passable both ways or are they one way valves. Is the new one I bought (air blows thru both ways) defective or is the original (air only goes one way) clogged and no good. Which one do I use and which way do I install it. Any diagrams showing which way the T goes and should air pass both ways or not. Thanks all for any input.

 

The original has a check valve in the line to hold vacuum in the system so the vacuum level doesn't dip during low manifold vacuum situations (high throttle angles). If I remember correctly, the black end connects to the line from the engine. From there, the other two ports go to the vacuum ball and then off to the vacuum accessories.

 

Thank you for your reply...while waiting for some input I stopped at the local junk yard and found a check valve on a 96 Jimmy which the man let me have for free.Now I have three to choose from. One from auto zone and two originals. Out of the two originals I do not know which one came off of my truck as I put them in the same pocket they are exactly alike. So,which one to use....
1.the auto zone one ( air can passe thru both ways on the connections that run from the ball to the engine.
2.one of the originals which is the same scenario has the auto zone one or..
3.the other original which air will not pass thru while blowing into the black side of the valve.

 

Are you blocking off the branch port (the one that is 90 degrees to the other two) when you are trying to blow through the check valve?

 

Yes I am and I just did a little test by filling a cup with water and with my thumb blocking/plugging the 90 degree end and blowing thru each of the other ends into the cup, this is what I found.
#1 original check valve... blowing thru each end is easy to do and produces considerable bubbles in the cup from each side.Free flowing thru each end.
#2 original check valve...blowing thru vac ball side is easy and produces considerable bubbles.Blowing thru the black/engine side of this check valve is very,very hard but I can produce very little/minimal bubbles in the cup.
So,am I to conclude #2 is partially clogged and defective or is this is the way it is supposed to operate or is #1 the correct operating check valve. Thank you very much for taking time to assist me.

 

Since the check valve is working with vacuum, sucking through it would be more appropriate, but not really advisable (LOL).

I'll describe the operation of the check valve under the conditions it sees in operation. Engine manifold vacuum is pulling air through the check valve towards the engine. This is the free flowing direction. When manifold vacuum drops below the vacuum level in the HVAC/4wd system, the check valve closes to keep air from returning into the system. They likely do not fully seat and seal so I would say your #2 is working properly and #1 is defective.

 

Check valve #2 put in and the truck is running just fine. I put #1 in for kicks and giggles and the truck just didn't run and feel right so I made the switch to #2. Of course I could have just did this in the beginning but I"m a guy who likes to ask questions and learn the why's and how's of how things work and operate which is why I joined this forum in the 1st place. Great place to learn to diagnose and repair the correct way instead of throwing time and money foolishly away. Thank you again for your time and comments.

 

No problem. Glad I was able to steer you in the right direction.