What is this and does it need to be hooked to a vacuum source - The 1947 - Present Chevrolet & GMC Truck Message Board Network

maxreps · 03-07-2009, 11:30 AM

Looking around behind the glove compartment area as I started putting my dash together I saw the heater/ac box with it's vacuum lines and manual controls... I followed a vacuum line that went through the firewall to see where it went and it was connected to the small round canister near on the firewall above the heater core lines. It also had a larger diameter hose coming out of it which I traced down to the A arm, dangling and unconnected.
I am assuming it's a vacuum canister for the heat/ac stuff in the cab but wanted to make sure.
Also, am I right in saying the line/hose coming out of the canister needs to be hooked to an engine vacuum source?

James McClure · 03-07-2009, 12:22 PM

In a word, YES. The cannister you see is a reserve for the AC & heat doors when you accelerate hard and vac drops. Hook it up to any manifold vac source. jim

maxreps · 03-07-2009, 04:42 PM

Thanks, will do. One question though, with it being disconnected does that mean the controls would not work properly if at all?

James McClure · 03-07-2009, 05:29 PM

The modes would be switched and possibly frozen into the defrost mode only (default) for saftey reasons. The mode switch (vacuum valve) in the control head gets it's vac supply from the reserve cannister. jim

maxreps · 03-07-2009, 11:39 PM

ok thanks for the info

03-07-2009, 11:30 AM	#1
maxreps Registered User Join Date: Jan 2009 Location: greensboro, nc Posts: 174	What is this and does it need to be hooked to a vacuum source Looking around behind the glove compartment area as I started putting my dash together I saw the heater/ac box with it's vacuum lines and manual controls... I followed a vacuum line that went through the firewall to see where it went and it was connected to the small round canister near on the firewall above the heater core lines. It also had a larger diameter hose coming out of it which I traced down to the A arm, dangling and unconnected. I am assuming it's a vacuum canister for the heat/ac stuff in the cab but wanted to make sure. Also, am I right in saying the line/hose coming out of the canister needs to be hooked to an engine vacuum source? Attached Images

03-07-2009, 12:22 PM	#2
James McClure One shot, one kill. Join Date: Dec 2007 Location: Saratoga Springs NY Posts: 859	Re: What is this and does it need to be hooked to a vacuum source In a word, YES. The cannister you see is a reserve for the AC & heat doors when you accelerate hard and vac drops. Hook it up to any manifold vac source. jim __________________ 1984 K20 350M engine with 465,000 miles. Well, it's finally done!! Almost 2 years of work, but it was really worth the effort. Little stuff left to do is mount winch, wet sand & buff out and build belly pan\running boards. Body work takes lots and LOTS of beer!!!! God, Guts and Guns made America and God, Guts and Guns will preserve it! The worst thing you could do is get into my sights, but that don't matter, you'll never know it, cause you'll never hear the shotJim or Paladin whichever you choose.

03-07-2009, 04:42 PM	#3
maxreps Registered User Join Date: Jan 2009 Location: greensboro, nc Posts: 174	Re: What is this and does it need to be hooked to a vacuum source Thanks, will do. One question though, with it being disconnected does that mean the controls would not work properly if at all?

03-07-2009, 05:29 PM	#4
James McClure One shot, one kill. Join Date: Dec 2007 Location: Saratoga Springs NY Posts: 859	Re: What is this and does it need to be hooked to a vacuum source The modes would be switched and possibly frozen into the defrost mode only (default) for saftey reasons. The mode switch (vacuum valve) in the control head gets it's vac supply from the reserve cannister. jim __________________ 1984 K20 350M engine with 465,000 miles. Well, it's finally done!! Almost 2 years of work, but it was really worth the effort. Little stuff left to do is mount winch, wet sand & buff out and build belly pan\running boards. Body work takes lots and LOTS of beer!!!! God, Guts and Guns made America and God, Guts and Guns will preserve it! The worst thing you could do is get into my sights, but that don't matter, you'll never know it, cause you'll never hear the shotJim or Paladin whichever you choose.

03-07-2009, 11:39 PM	#5
maxreps Registered User Join Date: Jan 2009 Location: greensboro, nc Posts: 174	Re: What is this and does it need to be hooked to a vacuum source ok thanks for the info



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