Vacuum Lines
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From: Salisbury
Vacuum Lines
In the process of getting everything cleaned up and fixed with the truck. I found two vacuum lines coming out of the fire wall. One bigger than the other.
Truck had factory AC and Heat. I'm guessing one of the lines is for adjusting the blend doors but what's the other one for? Heater control valve maybe?
Do they both go to manifold vacuum? The bigger one of em goes to vacuum canister and then comes out and hangs. Also are their any check valves in this routing I need to add? Thanks
Truck had factory AC and Heat. I'm guessing one of the lines is for adjusting the blend doors but what's the other one for? Heater control valve maybe?
Do they both go to manifold vacuum? The bigger one of em goes to vacuum canister and then comes out and hangs. Also are their any check valves in this routing I need to add? Thanks
Cargo Master
Joined: Nov 2011
Posts: 3,354
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From: Great American SouthWest
My 77 with dealer air doesn't have any vacuum lines into the cab.
My 78 and my 79 both have factory air, but each has only one vacuum line into the cab. Without vacuum to run things, all the a/c air goes to the defroster. The factory heater and a/c controls, one unit, are vacuum operated.
I don't know why you'd have a second vacuum line into the cab. Do you have cruise-control? Factory cruise control needs a vacuum line also, but that's in the engine compartment. You may also have a vacuum can on the driver fender under the hood
My 78 and my 79 both have factory air, but each has only one vacuum line into the cab. Without vacuum to run things, all the a/c air goes to the defroster. The factory heater and a/c controls, one unit, are vacuum operated.
I don't know why you'd have a second vacuum line into the cab. Do you have cruise-control? Factory cruise control needs a vacuum line also, but that's in the engine compartment. You may also have a vacuum can on the driver fender under the hood
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Senior User
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From: Salisbury
Originally Posted by PapaBearYuma
My 77 with dealer air doesn't have any vacuum lines into the cab.
My 78 and my 79 both have factory air, but each has only one vacuum line into the cab. Without vacuum to run things, all the a/c air goes to the defroster. The factory heater and a/c controls, one unit, are vacuum operated.
I don't know why you'd have a second vacuum line into the cab. Do you have cruise-control? Factory cruise control needs a vacuum line also, but that's in the engine compartment. You may also have a vacuum can on the driver fender under the hood
My 78 and my 79 both have factory air, but each has only one vacuum line into the cab. Without vacuum to run things, all the a/c air goes to the defroster. The factory heater and a/c controls, one unit, are vacuum operated.
I don't know why you'd have a second vacuum line into the cab. Do you have cruise-control? Factory cruise control needs a vacuum line also, but that's in the engine compartment. You may also have a vacuum can on the driver fender under the hood
Cargo Master
Joined: Nov 2011
Posts: 3,354
Likes: 48
From: Great American SouthWest
There used to be a device, possibly a check valve, up front on the line to the air cleaner, I think. There are no check valves now...but I pulled out a lot of stuff.
I have full-manifold vacuum lines for:
1) Automatic transmission
2) Power brake booster
3) A/C controls
4) Cruise control
And ported vacuum to the distributor
I have full-manifold vacuum lines for:
1) Automatic transmission
2) Power brake booster
3) A/C controls
4) Cruise control
And ported vacuum to the distributor
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Joined: Jul 2016
Posts: 198
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From: Salisbury
Well the big line goes behind the selector head unit and branches off into more lines that connect to the unit.
The one smaller line also goes behind the selector head unit but connects to the back of the top cold/warm lever and then comes back off and off somewhere else. I'm thinkin maybe it's for the door that opens and closes for recirculating cab or outside air.
Etheir way, I just hooked em both up to manifold vacuum and made sure for no leaks and left it be.
The one smaller line also goes behind the selector head unit but connects to the back of the top cold/warm lever and then comes back off and off somewhere else. I'm thinkin maybe it's for the door that opens and closes for recirculating cab or outside air.
Etheir way, I just hooked em both up to manifold vacuum and made sure for no leaks and left it be.
Cargo Master
Joined: Nov 2011
Posts: 3,354
Likes: 48
From: Great American SouthWest
Nice! Thanks for the diagram!
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