This was the culprit!
 

A few weeks back I had posted about a problem I was having with my defroster not working. Only place air would come out was the bottom vent. Also my A/C wasn't working. I had tried to determine the problem off and on over the next few weeks, but never could figure it out. This morning I went out and started tracing vacuum lines. I knew I wasn't getting any vacuum to the vacuum pod underneath the dash that controls the vents. Anyway I wound up pulling this check valve off and looking it over. Of course you can't really tell just by looking at it, so I went to the chevy dealer and got another one. Slipped it in and whala! Defroster is now working like a champ. Not only that but so is the A/C. But wait....there's more! My cruise control which had also been on the blink is now working like a new one. All of this for only $6.00 :) I'm posting this just in case any others out there ever have a problem like this. A good indicator that it is the check valve is if the vent system in the duct work quits working, A/C quits working, and cruise control quits working. This little check valve will cause all three of those things to happen. This check valve is located right near the distributor and it draws vacuum from the rear manifold vacuum port. Hope this helps somebody out sometime.

Re: This was the culprit!
 

Can you explain to me where the vacuum lines go that hook up to that check valve? I have one hose hooked up from the P.O. and my cruise hasnt worked since i bought the truck......One of the lines goes the the manifold vacuum? Off of the carburetor?

Thanks for the help!!!!
Jeremy

Re: This was the culprit!
 

Thanks for the info, I just put it into my memory bank.

Re: This was the culprit!
 

Let me see if I can remember. It's dark out there right now, but I may have to come back later and change this a little. There is a "T" fitting that screws into the manifold itself (not the carb), right behind the carb. The right side of that T (as you're looking at it from the front of the engine) has a vacuum line that runs straight back to the firewall and into that check valve. The check valve branch that sticks out to the side goes to the vacuum line that runs into the cab to supply vacuum to the heater ducts. The other port runs (I think, I'll have to check) to the vacuum pod that mounts to the fire wall over by the fender well. I don't think your cruise will work without vacuum to that pod. I know that on mind, I wasn't getting any vacuum to the vacuum pod and my cruise wasn't working. Once I changed out that check valve, EVERYTHING started working again as it should. Keep in mind now that this is for my '86 with 305 engine. Other year models may be a little different. I'll take some pictures for you tomorrow that'll show, a lot better than I can explain, where these lines run.
HTH

Re: This was the culprit!
 

I happened to take a look under my hood today. I have the check valve connected on 2 of the 3 sides. I am guessing the one side that's not hooked up feeds into the carb once I get the engine mounted back in. One side runs into the firewall and I traced the other one down to a black plastic ball against the firewall on the driver's side. On the side of the ball there is a tee half way down with nothing connected in to it. Is yours similar to that? What connects there? Thanks for all the help!!!!!

Jeremy

Re: This was the culprit!
 

Thanks, I have an 88 Suburban that all of a sudden the heater wouldn't change vents and the cruise control quit working, so I'm glad to see this thread, and I will try and locate this part and replace, Thanks again for someone out there having the same problem as me.

ANDY

Re: This was the culprit!
 

Sorry for not posting the pics I promised. The wife, daughter and I had run down to my mothers to spend a few days with the family, but we're back and if I can get out there sometime today between rain showers, I'll try to take a few pics that explain where all the lines go. Merry CHRISTmas to all you guys and gals.

Re: This was the culprit!
 

Jeremy, mine has the fitting in the very top of it. I would imagine there might be some difference depending on year models, so that could very well be where it connects to. If you have cruise, that very same line also feeds it. There is a T in the line that runs down to the cruise unit.

Re: This was the culprit!
 

I failed to mention that I have none of the emission equipment on my engine. I know that you mention a manifold vacuum port and that has been eliminated on my engine. I think one of the ports on the front of my edelbrock carb should replace that???? I know that vacuum is being created because if I plug in the hose that normally goes from the charcoal canister to the air cleaner I get a great deal of suction on one of the other hoses coming from the canister. Any ideas on running the vacuum lines with the aftermarket carb and intake?????

Thanks!!!!!
Jeremy

Re: This was the culprit!
 

If I am not mistaken, that check valve is not the only thing that can keep the defrosters from working. It can be any of the vacuum lines if they are leaking(or broke).
It seems those little plactic tubes can crack when they get old so if someone is having trouble, check to see if any are broken.

Re: This was the culprit!
 

I'm resurrecting a post a bit here...any idea where one can buy some new heater/vacuum line? That tiny plastic stuff seems cracked up on my truck. Can I just replace it with regular vacuum line? Also, does anyone have a picture of how the line attaches to the manifold? The line plastic line seems way to small to attached to that vacuum post! Am I missing something?
:confused:
I have the manifold vacuum post still intact (off course it's capped) but I do not have the black vacuum resovoir. All I have is about 3 inches of that black plastic line that comes out of the firewall.

Thanks guys!

Re: This was the culprit!
 

I slip regular rubber vacuum line onto the thin plastic line when it breaks. It works well.

Slonaker