A/C vacuum reservoir

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RC92234

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1973 Convertible, 351 4v CJ, C6, Mach 1 Decor options, power: steering, brakes and windows, a/c, Rally Pac gauges, Deluxe interior.
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Got to looking into the HVAC system, in particular the vacuum subset that powers all the dampers.  My a/c vacuum reservoir canister was just riding loose under the hood, half resting on the vapor capture canister.  And neither of it's two hoses were connected to anything other than the can itself.  Here's the curious thing:  hoses coming off the canister are large, maybe 1/4" or 3/8", but the hose that runs through the firewall to supply vacuum from the can to the in-dash HVAC control is *tiny*,  1/8" at best.  

To connect for testing the vacuum canister to a vacuum source and to the hvac control, I crammed the teensy hose from the hvac control into the larger hose coming from the reservoir canister and the other reservoir canister hose to the manifold port that also hosts the power brake vacuum (see diagram).  It worked!  Started the engine then ran the HVAC through all settings with the glove compartment opened so I can see the under dash vacuum motors moving.  That's progress.

However, questions: 
1)  Should there be a reducing connector from the canister's big hose to the little under-dash hose?  The teensy hose is way to small to connect to the A/C reservoir canister.  Or, something else?
2)  There seems to be a place behind and below the vapor canister where the a/c reservoir should reside, but I don't see how it's held in place.  For now it's just resting where it's crammed in but that's not a decent long term solution.  How and what does is attach to, I believe, the inner fender?

 

Screen Shot 2021-10-28 at 2.57.37 PM.jpg

 

Kilgon

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Got to looking into the HVAC system, in particular the vacuum subset that powers all the dampers.  My a/c vacuum reservoir canister was just riding loose under the hood, half resting on the vapor capture canister.  And neither of it's two hoses were connected to anything other than the can itself.  Here's the curious thing:  hoses coming off the canister are large, maybe 1/4" or 3/8", but the hose that runs through the firewall to supply vacuum from the can to the in-dash HVAC control is *tiny*,  1/8" at best.  

To connect for testing the vacuum canister to a vacuum source and to the hvac control, I crammed the teensy hose from the hvac control into the larger hose coming from the reservoir canister and the other reservoir canister hose to the manifold port that also hosts the power brake vacuum (see diagram).  It worked!  Started the engine then ran the HVAC through all settings with the glove compartment opened so I can see the under dash vacuum motors moving.  That's progress.

However, questions: 
1)  Should there be a reducing connector from the canister's big hose to the little under-dash hose?  The teensy hose is way to small to connect to the A/C reservoir canister.  Or, something else?
2)  There seems to be a place behind and below the vapor canister where the a/c reservoir should reside, but I don't see how it's held in place.  For now it's just resting where it's crammed in but that's not a decent long term solution.  How and what does is attach to, I believe, the inner fender?

 

View attachment 55907
The  canister should have a bracket attached to it.  Also, there should be both a large and small nipple on top for the vacuum hoses to connect to.  The small 1/8 line should fit directly on the canister.   See below pic.  Hope this helps.

Vacuum Canister (2).jpg

 
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RC92234

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1973 Convertible, 351 4v CJ, C6, Mach 1 Decor options, power: steering, brakes and windows, a/c, Rally Pac gauges, Deluxe interior.
[url=https://ibb.co/ZVjjKXW][img]https://i.ibb.co/zrMMbxG/s-l1600-2.jpg[/img][/url]
Excellent and thank you!  That explains the odd bracket there all by itself - lol. So, my can has come free from the bracket and the bracket is still attached to the inner fender.  Thing is... it has a horizontal orientation and the can would be on its side if mounted that way.  I'll look again more closely.  Also, I do have the two nipples on the top of the can but they are equal sized.  It doesn't look as if one has been broken or cut, and the hose that was on there came off as if it had been a long time.  It's currently the one hosting the much smaller hose that goes through the firewall.  What's left of the smaller hose is too short to reach where the can would go, but big hose + small hose does.

 

Kilgon

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Excellent and thank you!  That explains the odd bracket there all by itself - lol. So, my can has come free from the bracket and the bracket is still attached to the inner fender.  Thing is... it has a horizontal orientation and the can would be on its side if mounted that way.  I'll look again more closely.  Also, I do have the two nipples on the top of the can but they are equal sized.  It doesn't look as if one has been broken or cut, and the hose that was on there came off as if it had been a long time.  It's currently the one hosting the much smaller hose that goes through the firewall.  What's left of the smaller hose is too short to reach where the can would go, but big hose + small hose does.
Big hose to small will work.  Just get a inline connector reducer to join  the two.  Should be able to make a 1/4 to 1/8 or 3/16 to 1/8 work.  I don't think it matters if the cannister is upright but I would try to mount it that way.

 

Aus73Mach1

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Q code. 351-4V
C6 Auto, 3.25 Rear Axle, AC, Power steering.
I wasn't sure whether the vac can has a one way valve to hold vacuum once the engine was stopped. Mine certainly didn't so I installed a small one way valve in the vac line from the tree to the can. The system now holds vacuum and the vents, etc will operate a few times after the engine stops. It also verified no leaks in all the under dash vac lines.

20211030_105433.jpg

 

Kilgon

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That will work.  Attached is a pdf file on how to test the different vacuum motors and what vents are open or closed based on the control settings.

AC - Heater Vacuum Motors Testing.pdf

 

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  • AC - Heater Vacuum Motors Testing.pdf
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Aus73Mach1

Well-known member
Joined
Aug 5, 2019
Messages
126
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79
Location
QLD Australia
My Car
1973 Mach 1 Sports Roof.
Q code. 351-4V
C6 Auto, 3.25 Rear Axle, AC, Power steering.
Thanks Kilgon, that's a very helpful document.

So the check valve in the can is probably a thin piece of rubber and after so many years has probably deteriorated.

 
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