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Discussion Starter #1 (Edited)
Heater hose / heater core cut-off valve UPDATE W/PIC

Is there a cut-off valve supposed to be inline on one of the heater hoses to "disable" the heater core when it's not being used...so hot water isn't heating-up the core at all times? Working on a '72 Vette.
 

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Yeah, there's a vacuum operated valve in line with one of the heater hoses to the heater core.

However, even with the valve closed you're going to get some heat transfer thru the valve and into the heater core.

I replaced the OEM vacuum valve with a custom ordered ASCO 12VDC solenoid valve, (after the replacement OEM unit I tried first eventually rusted up). Never got around to hooking the solenoid to a vacuum switch, 'cause I got plenty of heat from the transfer thru the closed valve, (and I live in a desert, so don't really need any extra heat anyway).

To stop the heat transfer completely, you have to take the heater core out of the circuit, and loop the inlet/outlet hoses together.

I've also heard of some people putting in throttle valves (barb-to-barb brass garden variety with the round faucet handle) in line to cut off the flow manually, in both lines. But you still get heat transfer (and stagnant coolant sitting in the heater core when they're closed).

Sorry...prolly TMI! lol:D
 

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AC cars have the cut off valve, depending on model year. Non-AC usually do not have one.

You can add one. You can also purchase rubber caps which allow you to remove the hoses and cap off the lines on the engine.

:thumbsup:
 

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my 72 didn't have one and I bought the car back in '78. The '75 non ac cars we have did have them not sure when they started to come out but the one for a 75 should work if you get vaccuum to it. A simple little ball valve would do the same but wouldn't be "correct"
 

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Hmmm...where should it be located?
If you follow the routing of you heater hoses :

one runs from the water pump, under the AC compressor and runs down the pasenger frame rail into the bottom of the heater plentum

And the other runs from the front corner of the intake manifold under the AC compressor along the pasenger side frame rail with the other hose and into the bottom of the heater plentum. This valve should be located along that path between the frame rail and the heater box with no special routing of hose
 

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Discussion Starter #9
If you follow the routing of you heater hoses :

one runs from the water pump, under the AC compressor and runs down the pasenger frame rail into the bottom of the heater plentum

And the other runs from the front corner of the intake manifold under the AC compressor along the pasenger side frame rail with the other hose and into the bottom of the heater plentum. This valve should be located along that path between the frame rail and the heater box with no special routing of hose
I'm doing an LS1 swap, so my hose routings are different...but still should be very similar. I've routed the hoses and I don't remember seeing one of these valves along the way. Would the valve be mounted to the frame rail, to the fire wall, to the heater/AC box, etc?
 

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You will find it on the passanger side just below the heater fan motor in the wheel well just to the rear of the expantion tank.

You can get to it by removing the side louver...
 

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The stock valve on my 77 was right in the middle of the passenger side of the engine bay, in the same area as the expansion tank. It may have moved over the years.
 

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Discussion Starter #14
I think someone removed both my expansion tank and this valve as neither are anywhere to be found. :-/ No my problem is...where is the vacuum line that is supposed to operate it?
 

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...where is the vacuum line that is supposed to operate it?...
Routes from the AC console control, through the firewall, and over to the valve.

The assembly instruction manual (AIM) would help you. It has diagrams of the factory AC installation, including the vac hose routing and the location and plumbing for the cut off valve.

:thumbsup:
 

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Routes from the AC console control, through the firewall, and over to the valve.
:thumbsup:
Be aware that this vac line is (at least on a 78) a thin (1/8" OD?) white plastic hard line, (not rubber) that if original, is likely brittle and prone to breakage. You may not see more than a short piece protruding from the firewall, or even broken off at the firewall.
 

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Be aware that this vac line is (at least on a 78) a thin (1/8" OD?) white plastic hard line, (not rubber) that if original, is likely brittle and prone to breakage. You may not see more than a short piece protruding from the firewall, or even broken off at the firewall.
My '79 has a special grommet in the firewall. Inside the cabin and under the hood, it has standard vaccum line attached to that grommet. I don't have hard plastic.

Again, maybe years are different?
The '79's also had the vacuum valve above the frame on the passenger side near the radiator overflow tank. Right out in the open.
 

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Discussion Starter #18
Is it possible that my car didn't come with an expansion tank or heater control valve? I talked with a local Corvette guy yesterday and he said my car wouldn't have come with one...which makes sense based on what I'm seeing, ie; the holes where the expansion tank should be mounted were never drilled out. I'm also not seeing any sign that there ever was a heater control valve mounted anywhere. The final thing is, as mentioned above, the white line coming from the A/C control in the console doesn't go through the firewall, but rather to some kind of actuator on the back of the inside heater box. The only two hoses going through the firewall are black and green/black (see pic). Also, when I look on the firewall outside, the third hole, below black and gree/black is factory sealed...never punctured, for another hose.

Any help guys?


Untitled by clemson_tiger29679, on Flickr
 

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Discussion Starter #19
Is it possible that my car didn't come with an expansion tank or heater control valve? I talked with a local Corvette guy yesterday and he said my car wouldn't have come with one...which makes sense based on what I'm seeing, ie; the holes where the expansion tank should be mounted were never drilled out. I'm also not seeing any sign that there ever was a heater control valve mounted anywhere. The final thing is, as mentioned above, the white line coming from the A/C control in the console doesn't go through the firewall, but rather to some kind of actuator on the back of the inside heater box. The only two hoses going through the firewall are black and green/black (see pic). Also, when I look on the firewall outside, the third hole, below black and gree/black is factory sealed...never punctured, for another hose.

Any help guys?


Untitled by clemson_tiger29679, on Flickr
 
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