Vacuum lines for hvac system

[K5Rob]

The vacuum tank is needed. It is a reservoir so you have vacuum when the engine is not making vacuum. The check valve keeps the vacuum in the system and does not let it bleed off into the manifold.

That picture above is what I had found but it is not 100% correct for my 1987 V3500. The fitting in the intake connects a hard metal line to the vacuum modulator on the transmission. The metal line fits inside the fitting on the manifold.

Thank you. I have no transmission modulator or throttle/dist servo as i am running an Ls motor. Just need vacuum to actuate my hvac vents, mainly the defroster. Would my “A” drawing accomplish this?

 

[edgephoto]

Thank you. I have no transmission modulator or throttle/dist servo as i am running an Ls motor. Just need vacuum to actuate my hvac vents, mainly the defroster. Would my “A” drawing accomplish this?

No, the check valve needs to be in the line off the manifold before the Tee

 

[Poppy 87]

Ok guys thanks for all the info.

So here’s my issue, I have an LS and manifold vacuum sources are limited. I have one that goes to driver side valve cover, drawn in Green. Can I just Wye here, and run my OE lines as shown in Pink? (Drawing A) This option replicates the diagram posted by Broken85

Or is the Vac Tank even nescessary? Can I wye off the manifold and run directly to the dash control box? (Drawing B)

Pretty sure in the LS photo that is PCV, not manifold vacuum

 

[K5Rob]

Pretty sure in the LS photo that is PCV, not manifold vacuum

Poppy I hooked a vac gauge to this port and am getting 16” at idle. I was assuming its vacuum. It IS tied to the valve cover like a pcv. I dont know how the pcv system on an LS is laid out. Do you?

 

[K5Rob]

Okay well Ive got it figured out. Heres what i did, as a contribution to the site and the internet in general as there seems to be little info out there that I could find on LS vacuum accessory sources.

On the PS side of the truck intake approximately center there is actually a vacuum nipple with a moulded on cap that you can break, or twist off with pliers. This is what i used for vacuum source. I think this is the best option.

Then, as suggested above by you guys, I ran a check valve off the vacuum source, then a Tee to the ball reservoir on one side and the control box on the other. Everything seems to work now.

 

[Poppy 87]

PCV is typically post combustion gasses and is considered "dirty air" side. Preferred is "clean air side", direct intake manifold vacuum. LS intake has provision for brake booster, may need to tap into that, but be sure to plumb in a check valve so you don't loose brake assist.