Where do these vacuum lines go?

Where do these vacuum lines go?

Postby nubetoob [OP] » April 23rd 2017, 8:09pm

Hello. This is NOT a question regarding the main vacuum line which controls the vents (defrost, face, floor), I already changed that line and they're working great.
This question IS regarding the other two vacuum lines/hoses that come off that same T that the main vacuum line comes off.
*My question is: what are the other two lines for, and where do they go?*
In relation to my picture, the top line is broken and I'm unsure where it's supposed to plug in to. The middle line is the vacuum hose from my vents (it's working). And the bottom line goes into my firewall but I'm also hoping to figure out where it plugs into and what it is for. (I pulled off some plastics from my dash and still can't find where the hose comes through the firewall).
So in summary: what's the top line for. What's the bottom line for? And where/what do they plug in to.

I'm trying to fix my "no a/c problem, and I figured I'd start here with these lines. At least just to cure my own curiosity id like to know what their functions are.
Someone once told me that the top line is for 'rear a/c', but this is a gmc safari cargo and my intuition tells me that this system isn't equipped for a rear a/c, so it must be for something else.

I appreciate any help or feedback. And if anyone has a diagram of how the a/c system works on these vans that would be helpful. Also if you know of a good write-up regarding the a/c on astrosafari.com I would love to have a link to that.
Thanks!
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Re: Where do these vacuum lines go?

Postby AstroWill » April 23rd 2017, 8:30pm


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Re: Where do these vacuum lines go?

Postby MI_Ghost » April 23rd 2017, 9:58pm

I will start by clearing up a few things.
That top line with the elbow is the vacuum line that would normally go to the port on the driver side of the engine. The lines have been switched on your T fitting. The T fitting normally sits behind the AC dryer along the cover for the heater core.

The hose off the bottom of the T fitting would run down below the AC dryer/Alternator to the round ball which is just a vacuum storage tank.

The last line runs to the heater controls on the dash. It gets routed up behind all the ducts under the dash and will be impossible to trace without pulling the dash and ducts apart. There will be connector on the back or the heater controls that it goes to.

The rear AC does not have any changing vents. It would not use any vacuum controls. Just electrical for the fan speeds.
For rear AC there would be a big black box and duct in the driver side rear corner of the van and a fan speed switch to the right of the heater control panel.
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Re: Where do these vacuum lines go?

Postby sixsix » April 23rd 2017, 10:28pm

I am thinking you need to look for the "Vacuum Ball" - it's down there near the upper control arm front mount.
Hard to see it under the hood w/o removing "Loads Of Vinyl" shrouds, air inlet, etc.
Some say it is easier to see / find by looking in the front pass. wheel well under the splash guard.

:confused:

Mike

ps: I have photos of our 92' Vacuum Ball - but from the engine bay -
. . .I had all that crap mentioned above - removed.
. . .The Van has a different vac. system from Will's drawing, but the "Ball" is similar.
.

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Re: Where do these vacuum lines go?

Postby nubetoob [OP] » April 24th 2017, 3:15am

MI_Ghost wrote:I will start by clearing up a few things.
That top line with the elbow is the vacuum line that would normally go to the port on the driver side of the engine. The lines have been switched on your T fitting. The T fitting normally sits behind the AC dryer along the cover for the heater core.

The hose off the bottom of the T fitting would run down below the AC dryer/Alternator to the round ball which is just a vacuum storage tank.

The last line runs to the heater controls on the dash. It gets routed up behind all the ducts under the dash and will be impossible to trace without pulling the dash and ducts apart. There will be connector on the back or the heater controls that it goes to.

The rear AC does not have any changing vents. It would not use any vacuum controls. Just electrical for the fan speeds.
For rear AC there would be a big black box and duct in the driver side rear corner of the van and a fan speed switch to the right of the heater control panel.


Wow. That changes things. So first of all...
Regarding that top line that is chopped off. I started my vehicle today with this broken line unplugged and I did NOT feel any suction when I placed my finger on the plastic T where it plugs in to. So if I were to plug my vac line to it, the one that plugs into the port on the drivers side of my engine, I'm guessing I wouldn't be able to control my vents. Yeah, if it ain't broke, don't fix it. But I just want things to be where they're supposed to be because I'm about to start trouble shooting my 'no a/c' issue.
However, maybe I didn't feel any suction because it had the other 'middle' line, which was still plugged in, taking all the suction. I will cap it and switch lines to see what happens.

Regarding the bottom plug that goes into the firewall... thanks for the info because I already took off a few of the smaller dash plastics and duct work and still wasn't able to spot the other end. I think I will forget about this hose for now and cross my fingers that it's routed where it's supposed to be. I will at least change the small piece of line that goes from the bottom of that T fitting to the firewall since it is old and crumbling.

And I will just try and locate the "vacuum ball thingy" (you know, the thingy), and see if it's plugged in to anything. If not, i will run the middle port to that.
What the heck is that ball thing for anyway?
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Re: Where do these vacuum lines go?

Postby Leeann_93Leeann_93 is online! » April 24th 2017, 3:17am

It's a reservoir. So if your engine isn't making good vacuum, like under heavy load, you still have vacuum for vacuum-run accessories.
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Re: Where do these vacuum lines go?

Postby nubetoob [OP] » April 24th 2017, 4:48am

Leeann_93 wrote:It's a reservoir. So if your engine isn't making good vacuum, like under heavy load, you still have vacuum for vacuum-run accessories.


I appreciate all the info. I just found my vacuum reservoir ball and nothing was plugged in to the little 'nipple' on it.
I've been chasing a vacuum leak for a while now....
Do you think it's possible this vacuum reservoir being unplugged would cause a small vacuum leak?
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Re: Where do these vacuum lines go?

Postby MI_Ghost » April 24th 2017, 4:59am

The T fitting has a check valve built into it. This allows vacuum to be pulled in one direction only. The way it is now it is pulling against the backside of the valve closing off that port. With vacuum applied to check valve port you will get a vacuum signal to the other two ports.

Once you get past the firewall the rubber and plastic hoses are not exposed as much to the conditions that cause them to dry rot and deteriorate. Unless one of the vent valves is not working at all. It in not worth the effort it would take to replace the hose any further.

As Leeann noted. The ball is just a storage tank for low vacuum conditions.
With the way your hoses are connected right now. If you quickly floor the gas pedal your dash vents will cut out. The ball keeps this from happening.
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Re: Where do these vacuum lines go?

Postby nubetoob [OP] » April 24th 2017, 7:26am

MI_Ghost wrote:The T fitting has a check valve built into it. This allows vacuum to be pulled in one direction only. The way it is now it is pulling against the backside of the valve closing off that port. With vacuum applied to check valve port you will get a vacuum signal to the other two ports.

Once you get past the firewall the rubber and plastic hoses are not exposed as much to the conditions that cause them to dry rot and deteriorate. Unless one of the vent valves is not working at all. It in not worth the effort it would take to replace the hose any further.

As Leeann noted. The ball is just a storage tank for low vacuum conditions.
With the way your hoses are connected right now. If you quickly floor the gas pedal your dash vents will cut out. The ball keeps this from happening.


Great info! I'm bummed though because I was hoping that that vacuum reservoir being unplugged was the cause of my vacuum leak. (Hesitation in idle, also throwing a P0304 cylinder 4 misfire). Sounds like it won't fix any of that... but at least I can scratch it off the list and move on. It's an easy fix.
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Re: Where do these vacuum lines go?

Postby AstroWill » April 24th 2017, 6:59pm

Yep, set it up like the diagram, and you should be good to go. Also those check valves do go bad over time, you should check yours.

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Re: Where do these vacuum lines go?

Postby Don1806 » April 26th 2017, 11:33pm

I'm still confused after reading these posts. Is one of those hoses going to Heater Control Valve? (I didn;t see it mentioned in any of these posts.)

if so, you need to check and make sure you have a solid connection there and that it's not sucking air. If not, then your heat is running full time.

As the others have said though, the diagram will not fail you. Your heater control valve may.
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Re: Where do these vacuum lines go?

Postby nubetoob [OP] » April 27th 2017, 6:23am

Don1806 wrote:I'm still confused after reading these posts. Is one of those hoses going to Heater Control Valve? (I didn;t see it mentioned in any of these posts.)

if so, you need to check and make sure you have a solid connection there and that it's not sucking air. If not, then your heat is running full time.

As the others have said though, the diagram will not fail you. Your heater control valve may.

I didn't mention my heater control valve because she's been plugged in and working since I bought the van. There are two hoses from the firewall. One running to the check valve and one running to the heater control valve.
I do have heat. It was weird though, when I first bought the van I didn't have heat. After looking at some pics online I determined it was installed upside down so I flipped the heater control valve and viola, heat. And then literally 1 week later my brand new heater control valve started pissing out coolant. So anyway I returned it, slapped a new one on in the same manner and it's been working ever since.
I got all my lines hooked up and working properly.. I appreciate you looking out though.
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