Hey everyone. I have to hook up vaccum lines on my 87 Trans AM. Its officially an LS1 car...and I have the FAST intake. I have two vaccum ports...I think... Now... What I need to know is, what needs vaccum on the car now.

I have two hard vac. lines coming from my fire wall. They come from the same place that the HVAC wires are. I figured one is for the vents..but dont know what the other is for. I know I have to hook up the vac. canster that is under teh batter try too...

As far as I know thats all I need. I just need to know what the heck the two lines are for coming from the firewall. Can anyone give me a hand? Thanks in advance for any input!

Justin

 

One is to supply engine vacuum to the HVAC system under the dash. I beleive that one is shorter and has a 90* hose nipple on the end. That's gotta hook to manifold vacuum. Start to finish.... A vacuum hose went from an engine manifold vacuum port through a vacuum check valve (one-way valve, small, pointy on one end) then through a T (which was built into the back of the check valve, I believe). One side of the T went to this 90* vacuum connector into a vacuum hardline and under the dash to the HVAC selector switch. The other side of the T went to a rubber vacuum line that connected to the "sphere of power" (vacuum reservoir) in the fender up front. In other words, both that HVAC vacuum hose and the vacuum reservoir were on the same line, behind a vacuum check valve.

The other one is longer and has a straight nipple on the end. That one USED TO run the heater core bypass valve on your old engine to turn off coolant flow through the heater core any time you pushed the HOT-COLD selector all the way to cold. I'm guessing you don't have anything like that valve on your LS-1 transplant, so you can just plug it and tuck it.

 

Ah yes... I totally forgot about the heater control valve!!! Thanks!!! SO I can disconnect that inside from the HVAC controls? Or does it have to be capped off. Ill check it out because I have the HVAC controls out right now. Ide like to atleast pull the hose inside if I dont need it. Less clutter.

So its sounds like all I need to do is hook up that one line to the back of the intake. Then hook up my gauge to the other fitting on the intake...my vac. gauge that is.

Now...one more question. The check valve...where is it keeping vacuum? Is it keeping it from flowing in one direction to the HVAC controls? Or to somethign else. In other words...whats teh one way check valve doing. I just want to hook it up correctly so that everything gets the vac that it needs...and its not blocking the vac. from something else.

I also have to hook up the "power orb"... the thingy that holes vac. with the motor off.

Thanks again for the help!

Justin

 

You need to plug the heater control vacuum line. Any time you switch it to "cold" it'll apply vacuum to that line.

The one-way vacuum valve only allows air to flow TOWARDS the engine. In other words, it holds vacuum at the HVAC controls/vacuum reservoir even when engine vacuum drops down very low (Wide Open Throttle, for instance). If you get it turned around the wrong way you'll know it- you'll only get air blowing out the Defrost vents- 3rd gens default to blowing out those vents in no vacuum is present to move the HVAC doors uner the dash.