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79Chevypickup · 10-10-2003, 11:10 AM

Can someone please tell me what this round black thing is for?
The next pic is of a hose that is connected to it, but
it is not connected to anything else..

79Chevypickup · 10-10-2003, 11:12 AM

Do you know what this is supposed to go to?

**N2TRUX** · 10-10-2003, 11:25 AM

That's a vacuum canister. The line you are holding should be connected to a multi-tap fitting on the top of the intake manifold, behind the carb.

There should be a small hard plastic line coming out of the bottom of the ball, going through the firewall. I "believe" that line goes to the vent/defrost door actuator....

Prerunner1982 · 10-10-2003, 11:26 AM

you have A/C? i have one but its a sphere. i think its A/C or heater related....

damn... a dollar short and a day late (see user text)... i was close...

79Chevypickup · 10-10-2003, 11:27 AM

so this could possible be the reason why my defroster doesnt work?

79Chevypickup · 10-10-2003, 11:32 AM

The plastic post that is on my intake has to places to connect a hose, but
There is one hose that connects it to itself, you know what I mean?
There is a top stub and a stub on the left, well
the one hose is on both....

Is it supposed to be like that or ???????

**crossy** · 10-10-2003, 11:36 AM

that looks like the vacuum booster . neither one of my NON A/C trucks have it and the vacuum routing book I have here shows 28 DIFFERENT vacuum hose routings for 1980 trucks (it only goes back to 80 but should be the same as a 79) and none of them show a booster . Basically that booster is for storing an extra amount of vacuum needed for certain controls., especially on A/C trucks, It should have a MAIN supply of vacuum running to it right from the intake manifold and then go out and 'T' into other sources that need vacuum.'
Swervin & goodwrench are both real good at 'what works what'. DAVE

79Chevypickup · 10-10-2003, 11:39 AM

my truck has A/c but it doesnt have all the components for it, so it doesnt work....

N2TRUX was saying that the hose is supposed to connect to the intake, but there already is a hose there a single hose that connects to both connections....
is this right?

as I am sure you are aware of... I am trying to fix my defroster and I wasnt sure if this had anything to do with the vacum system

**crossy** · 10-10-2003, 11:43 AM

Quote:

Originally posted by 79Chevypickup
my truck has A/c but it doesnt have all the components for it, so it doesnt work....

as I am sure you are aware of... I am trying to fix my defroster and I wasnt sure if this had anything to do with the vacum system

yes, i see that it does have A/C now. and YES it has a hell of a lot to do with what works inside the truck because i mentioned in your other post about defrosters that A/C equipped trucks have the MAIN switch works off of vacuum.

**crossy** · 10-10-2003, 11:46 AM

isn't there a vacuum hose that disappears through the firewall behind the distributor? it's tough for me not having an /c truck here right now to lok at but there should be a main line that runs through the firewall into the cab and to the back of your main heat/AC switch. DAVE

79Chevypickup · 10-10-2003, 11:55 AM

man, I cant figgen tell or see....
is that hose supposed to connect to the main line or the intake ?

**crossy** · 10-10-2003, 12:01 PM

just ell me if there is a main line running through the firewall, if there is bypass the 'black ball' and take the vacuum line running through the firewall and hook it directly to amnifold source. usually right behind the carb, then check inside to see if your defroster work. HINT *engine must be running. :-)

79Chevypickup · 10-10-2003, 12:03 PM

check out these three pics!!
here is the hose ontop of the intake

79Chevypickup · 10-10-2003, 12:04 PM

Here is a hole going through the firewall, but it is not behind the distributer

**crossy** · 10-10-2003, 12:15 PM

Quote:

Originally posted by 79Chevypickup
Here is a hole going through the firewall, but it is not behind the distributer

, thats OK I was going by my NON existent memory.

WAHAAAAAAAAAA , dude look at that main source fitting on the back of your manifold , it has a big loop in it and goes NOWHERE! one of those should run to the bigger fitting on the black ball as a SOURCE then from the black ball that small hard black line that runs through the firewall is what supplys your switch inside. buy 4' of vacuum line(probably 5/32") and run a new line to the ball , from the manifold fitting. plug the other outlet on the mainfold fitting for now until we figure out what someon e disconnected there.

79Chevypickup · 10-10-2003, 12:23 PM

Alright crossy, dont go anywhere I am gonna go try it out!!

79Chevypickup · 10-10-2003, 12:34 PM

Alright there is progress!!!
A little bit and I mean a little....
bit of air comes through the top....
Finnally...
How can I make it as strong as the other vents?
even on defroster air come out the other vents
besides the top...
do you think its a bad distribution box?

Prerunner1982 · 10-10-2003, 12:55 PM

even with switch on high, only alittle air comes out the defroster?

79Chevypickup · 10-10-2003, 01:15 PM

Yes, this is correct!!

MylilBowTie · 10-10-2003, 01:28 PM

On mine that's where the vacuum ball hooks up and the modulator valve line connects. The black vacuum ball has a check valve and its just stores vacuum for use by the heating and a/c system. Its what opens and closes all the doors to reroute the air. The line that goes in the truck cab should be near the heater blower area or on the other side of the black a/c box on the firewall.

But it does blow more out on the other vents? I would try cleaning the wires the go to the heater blower motor. If its not that its just not getting enough vacuum for some reason. Lines might have cracks in them or something like that. Could be old and collapsing on themeless too.

**crossy** · 10-10-2003, 02:34 PM

I had to check out a while, won't be back much more today but you basically found the problem. since things do work somewhat now you can get your hand back there on the arms and see what is working and which way it goes when the stuff works. and they may just need adjusting . the defrost may not be working fully right now because there is also a hidden flapper under the passenger side vented cowling (outside) that either opens or closes(memory again) when differnt switches are activated . My point is that the silver vacuum pods/flappers all work off of vacuum on an A/C truck. Defrost always works better running down the road .
Go inside the truck Listen to your heat/AC switch real good inside the truck when it's running and see if notice a hissing/sucking noise at the switch. like i mentioned before it is not uncommon for the seal in that switch to go bad . I also noticed that your engine has an aftermarket carb/intake combo, does it have a big cam in it ? they cause low vacuum, and if it is not holding good vacuum at idle it may not be enough. stock engines hold 15-20 in. at idle . get the ball hooked back up and see how you do then.
I also had a problem once with that small hard black line that runs inside had a pinhole leak in it. you'll get it now. DAVE

79Chevypickup · 10-10-2003, 02:42 PM

Thanks DAVE and to all who posted!!!

I appreciate everyones help!!

1985K10 · 10-10-2003, 06:18 PM

My truck w/AC, my 84,and 86 w/o AC all have that Vacuum reserve thing. All came stock with a 305. (mine has a 350 now) They are all sphere shaped, and mounted near the driverside fender on the firewall, with one hose going to them.

**N2TRUX** · 10-10-2003, 07:49 PM

79Chevypickup,
Let me make sure you are on track here. That line coming off the ball should go to the fitting you have pictured. On my 77, the other port on that fitting goes to a short rubber line that is connected to a metal line. It dissapers behind everything, so I'm not sure where it goes. We can get back to that later.

For now, one port should be connected to the line leading to the vacuum canister. The other port should be blocked off if it's not connected to anything. Put a screw or bolt in the short piece og line you have there, unless you have some vacuum port caps.

This should open the flap to your defrost, and close it from flowing to the other vents.

Let me know how this goes, and we can go from there...

**N2TRUX** · 10-10-2003, 07:56 PM

Ok, I just re-read Crossy's post, and realized he told you the same thing already. Just for reference, I highlited the line that comes off of the canister and goes to the control box.
Follow this line inside, and it should lead you to the control box. At the point of connection, you could have a leak there.

Let us know how it goes...

10-10-2003, 11:10 AM	#1
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	What is this? Can someone please tell me what this round black thing is for? The next pic is of a hose that is connected to it, but it is not connected to anything else.. Attached Images __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E

10-10-2003, 11:12 AM	#2
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	Here is the hose Do you know what this is supposed to go to? Attached Images __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E

10-10-2003, 11:25 AM	#3
N2TRUX Happy to be here Join Date: Mar 2000 Location: Cypress, TX Posts: 39,023	That's a vacuum canister. The line you are holding should be connected to a multi-tap fitting on the top of the intake manifold, behind the carb. There should be a small hard plastic line coming out of the bottom of the ball, going through the firewall. I "believe" that line goes to the vent/defrost door actuator.... __________________ Follow me on Facebook and Instagram @N2trux.com Articles- "Jake" the 84 to 74 crewcab "Elwood" the77_Remix 85 GMC Sierra "Scarlett" "Refining Sierra"

10-10-2003, 11:26 AM	#4
Prerunner1982 Registered User Join Date: Oct 2002 Location: Edmond, OK Posts: 5,906	you have A/C? i have one but its a sphere. i think its A/C or heater related.... damn... a dollar short and a day late (see user text)... i was close... __________________ Jon 1982 Chevy Silverado 350/th350.... RETIRED 1993 Jeep XJ 2 door(Cherokee) 4wd 4.0ltr/AX-15 (5spd)/NP231 .... Oklahoma Roll Call Last edited by Prerunner1982; 10-10-2003 at 11:32 AM.

10-10-2003, 11:27 AM	#5
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	so this could possible be the reason why my defroster doesnt work? __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E

10-10-2003, 11:32 AM	#6
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	N2TRUX The plastic post that is on my intake has to places to connect a hose, but There is one hose that connects it to itself, you know what I mean? There is a top stub and a stub on the left, well the one hose is on both.... Is it supposed to be like that or ??????? __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E

10-10-2003, 11:36 AM	#7
crossy Oh,you can't buy that new Join Date: Apr 2000 Location: Pennsville,N.J. 08070, USA Posts: 2,039	that looks like the vacuum booster . neither one of my NON A/C trucks have it and the vacuum routing book I have here shows 28 DIFFERENT vacuum hose routings for 1980 trucks (it only goes back to 80 but should be the same as a 79) and none of them show a booster . Basically that booster is for storing an extra amount of vacuum needed for certain controls., especially on A/C trucks, It should have a MAIN supply of vacuum running to it right from the intake manifold and then go out and 'T' into other sources that need vacuum.' Swervin & goodwrench are both real good at 'what works what'. DAVE __________________ "been there, done that, ruined the T-shirt". 2007 LBZ GMC Sierra, ECSB 2006 LM7 RCSB Silverado 98 Vortec project. 94,3500,6.5L 4L80 81 SWB GMC POS finally gone 73 Pinto, stock, w/CragarSS's-eww LOTS of Cummins trucks. Last edited by crossy; 10-10-2003 at 11:41 AM.

10-10-2003, 11:39 AM	#8
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	crossy my truck has A/c but it doesnt have all the components for it, so it doesnt work.... N2TRUX was saying that the hose is supposed to connect to the intake, but there already is a hose there a single hose that connects to both connections.... is this right? as I am sure you are aware of... I am trying to fix my defroster and I wasnt sure if this had anything to do with the vacum system __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E

10-10-2003, 11:46 AM	#10
crossy Oh,you can't buy that new Join Date: Apr 2000 Location: Pennsville,N.J. 08070, USA Posts: 2,039	isn't there a vacuum hose that disappears through the firewall behind the distributor? it's tough for me not having an /c truck here right now to lok at but there should be a main line that runs through the firewall into the cab and to the back of your main heat/AC switch. DAVE __________________ "been there, done that, ruined the T-shirt". 2007 LBZ GMC Sierra, ECSB 2006 LM7 RCSB Silverado 98 Vortec project. 94,3500,6.5L 4L80 81 SWB GMC POS finally gone 73 Pinto, stock, w/CragarSS's-eww LOTS of Cummins trucks.

10-10-2003, 11:55 AM	#11
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	man, I cant figgen tell or see.... is that hose supposed to connect to the main line or the intake ? __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E

10-10-2003, 12:01 PM	#12
crossy Oh,you can't buy that new Join Date: Apr 2000 Location: Pennsville,N.J. 08070, USA Posts: 2,039	just ell me if there is a main line running through the firewall, if there is bypass the 'black ball' and take the vacuum line running through the firewall and hook it directly to amnifold source. usually right behind the carb, then check inside to see if your defroster work. HINT *engine must be running. :-) __________________ "been there, done that, ruined the T-shirt". 2007 LBZ GMC Sierra, ECSB 2006 LM7 RCSB Silverado 98 Vortec project. 94,3500,6.5L 4L80 81 SWB GMC POS finally gone 73 Pinto, stock, w/CragarSS's-eww LOTS of Cummins trucks.

10-10-2003, 12:03 PM	#13
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	crossy check out these three pics!! here is the hose ontop of the intake Attached Images __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E

10-10-2003, 12:04 PM	#14
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	Here is a hole going through the firewall, but it is not behind the distributer Attached Images __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E

10-10-2003, 12:23 PM	#16
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	Alright crossy, dont go anywhere I am gonna go try it out!! __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E

10-10-2003, 12:34 PM	#17
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	Alright there is progress!!! A little bit and I mean a little.... bit of air comes through the top.... Finnally... How can I make it as strong as the other vents? even on defroster air come out the other vents besides the top... do you think its a bad distribution box? __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E



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10-10-2003, 12:55 PM	#18
Prerunner1982 Registered User Join Date: Oct 2002 Location: Edmond, OK Posts: 5,906	even with switch on high, only alittle air comes out the defroster? __________________ Jon 1982 Chevy Silverado 350/th350.... RETIRED 1993 Jeep XJ 2 door(Cherokee) 4wd 4.0ltr/AX-15 (5spd)/NP231 .... Oklahoma Roll Call

10-10-2003, 01:15 PM	#19
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	Yes, this is correct!! __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E

10-10-2003, 01:28 PM	#20
MylilBowTie Right turn Clyde Join Date: Nov 2002 Location: Cincinnati, Ohio Posts: 2,911	On mine that's where the vacuum ball hooks up and the modulator valve line connects. The black vacuum ball has a check valve and its just stores vacuum for use by the heating and a/c system. Its what opens and closes all the doors to reroute the air. The line that goes in the truck cab should be near the heater blower area or on the other side of the black a/c box on the firewall. But it does blow more out on the other vents? I would try cleaning the wires the go to the heater blower motor. If its not that its just not getting enough vacuum for some reason. Lines might have cracks in them or something like that. Could be old and collapsing on themeless too. Last edited by MylilBowTie; 10-10-2003 at 01:31 PM.

10-10-2003, 02:34 PM	#21
crossy Oh,you can't buy that new Join Date: Apr 2000 Location: Pennsville,N.J. 08070, USA Posts: 2,039	I had to check out a while, won't be back much more today but you basically found the problem. since things do work somewhat now you can get your hand back there on the arms and see what is working and which way it goes when the stuff works. and they may just need adjusting . the defrost may not be working fully right now because there is also a hidden flapper under the passenger side vented cowling (outside) that either opens or closes(memory again) when differnt switches are activated . My point is that the silver vacuum pods/flappers all work off of vacuum on an A/C truck. Defrost always works better running down the road . Go inside the truck Listen to your heat/AC switch real good inside the truck when it's running and see if notice a hissing/sucking noise at the switch. like i mentioned before it is not uncommon for the seal in that switch to go bad . I also noticed that your engine has an aftermarket carb/intake combo, does it have a big cam in it ? they cause low vacuum, and if it is not holding good vacuum at idle it may not be enough. stock engines hold 15-20 in. at idle . get the ball hooked back up and see how you do then. I also had a problem once with that small hard black line that runs inside had a pinhole leak in it. you'll get it now. DAVE __________________ "been there, done that, ruined the T-shirt". 2007 LBZ GMC Sierra, ECSB 2006 LM7 RCSB Silverado 98 Vortec project. 94,3500,6.5L 4L80 81 SWB GMC POS finally gone 73 Pinto, stock, w/CragarSS's-eww LOTS of Cummins trucks.

10-10-2003, 02:42 PM	#22
79Chevypickup MY TRUCK IS FOR SALE!! Join Date: Sep 2003 Location: Pasadena, TX Posts: 292	Thanks DAVE and to all who posted!!! I appreciate everyones help!! __________________ 1979 Chevy LWB 350ci / 700R4 Edelbrock under the hood F O R S A L E OR T R A D E

10-10-2003, 06:18 PM	#23
1985K10 Registered User Join Date: Oct 2003 Location: CT Posts: 315	My truck w/AC, my 84,and 86 w/o AC all have that Vacuum reserve thing. All came stock with a 305. (mine has a 350 now) They are all sphere shaped, and mounted near the driverside fender on the firewall, with one hose going to them. __________________ Anthony 07 Tahoe LT 70 Chevelle 450HP 383-TH400 77 GMC Royal Sierra~Resto in progress~

10-10-2003, 07:49 PM	#24
N2TRUX Happy to be here Join Date: Mar 2000 Location: Cypress, TX Posts: 39,023	79Chevypickup, Let me make sure you are on track here. That line coming off the ball should go to the fitting you have pictured. On my 77, the other port on that fitting goes to a short rubber line that is connected to a metal line. It dissapers behind everything, so I'm not sure where it goes. We can get back to that later. For now, one port should be connected to the line leading to the vacuum canister. The other port should be blocked off if it's not connected to anything. Put a screw or bolt in the short piece og line you have there, unless you have some vacuum port caps. This should open the flap to your defrost, and close it from flowing to the other vents. Let me know how this goes, and we can go from there...

10-10-2003, 07:56 PM	#25
N2TRUX Happy to be here Join Date: Mar 2000 Location: Cypress, TX Posts: 39,023	Ok, I just re-read Crossy's post, and realized he told you the same thing already. Just for reference, I highlited the line that comes off of the canister and goes to the control box. Follow this line inside, and it should lead you to the control box. At the point of connection, you could have a leak there. Let us know how it goes... Attached Images __________________ Follow me on Facebook and Instagram @N2trux.com Articles- "Jake" the 84 to 74 crewcab "Elwood" the77_Remix 85 GMC Sierra "Scarlett" "Refining Sierra"

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