Photo of original heater control valve install?

[davepl]

Someone had long since removed the heater control valve from my 1970 GMC 402 with AC. I bought a reproduction, but does anyone have a photo of an original so I can see how its mounted, where it's spliced into the hose, and so on?

Thanks!
Dave

[gcburdic]

ttt

[NoNeck]

Dave -

Maybe you can get an idea from this photo from my son's '70 GMC with AC. It is a 350, but I don't think there is any difference in the way the hoses route. It appears that the valve goes between the top hose on the suitcase and the hose going to the intake manifold. I hope it helps.

NoNeck

[davepl]

Thanks! Can't quite see where it bolts... to the exhaust manifold, or inner fender?

[NoNeck]

It bolts to the inner fender. If it's the original AC inner fender, it should have two small holes about midway. If the inner has been replaced, most of them will have two small dimples (you have to look closely for them) that you can drill corresponding holes.

NoNeck

[1972SUPERSB]

I was wondering this myself. Looks like a vacuum hose goes to it. Where does the vacuum hose go to? What was the purpose of this valve?
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[73CheyenneSuper20]

[IMG] /IMG]
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71 3/4 ton with the big block 402
There is only 1 spot for a vacuum line, the lower 1 is solid.
I guess that it generally stops hot antifreeze from going to the heater core until you turn on the heat ....

[Luis_gz06]

What are the correct mounting screws for the valves?

[48richard]

The vacuum hose goes to the A/C control. When it is set to "Inside Air" the heater valve is closed.

[Andy4639]

This is out of the manual. Hope it helps sorry it doesn't say what size screws to use.

[SonomaComa]

Is that valve required if the truck does not have A/C?

[davepl]

I don't think so, and the heater-only controls don't have the vacuum switch to control it.

[Davidf]

Originally Posted by NoNeck

Dave -

Maybe you can get an idea from this photo from my son's '70 GMC with AC. It is a 350, but I don't think there is any difference in the way the hoses route. It appears that the valve goes between the top hose on the suitcase and the hose going to the intake manifold. I hope it helps.

NoNeck

This photo really confuses me. I see the a/c compressor, but the rest of the components don't seem right. A/C trucks have the evaporator under the hood and the heater core inside the cabin. This photo only shows a heater core under the hood. It seems this photos shows a dealer installed aftermarket a/c system???? I'm still confused.

BTW, I agree, no water valve if no a/c. Factory heater setup had water flowing through heater core 100% of the time.

[Andy4639]

This picture is not of a Factory AC box at all. It may have been a add on at the dealership are by some one after buying it but it's not the factory AC fire wall box, that's a factory non AC heater only box.
It has either a aftermarket AC unit are a dealer under dash unit installed.





Here is a factory AC setup for a 71-72 Chevy truck.
You can see the valve even though it's not positioned in the factory spot on the fender. I wanted it further down.

[71CHEVYSHORTBED402]

Two tapered body screws with integrated washers to RH inner fender, vacuum side front. Here's some nice info. on the vacuum config. if you need it (POST #3): http://67-72chevytrucks.com/vboard/s...=1#post7350337

[F.A.A.benny]

Originally Posted by Davidf

This photo really confuses me. I see the a/c compressor, but the rest of the components don't seem right. A/C trucks have the evaporator under the hood and the heater core inside the cabin. This photo only shows a heater core under the hood. It seems this photos shows a dealer installed aftermarket a/c system???? I'm still confused.

BTW, I agree, no water valve if no a/c. Factory heater setup had water flowing through heater core 100% of the time.

I was wondering the same thing. Interesting

[davepl]

Between the time I asked this in 2012 and now in 2015 wrapping it up, I managed to install it backwards, discover no heat, have someone notice it, and come back to this thread to confirm it was wrong.

You'd think I would have just installed it correctly the first time, but no. Just following up in case anyone wonders if it even matters, and it appears that it does!

[Andy4639]

You can't hook the valve up backwards! You can hook it to the wrong vacuum source though. Depending on which control head you use will detirm if it works are not.

[davepl]

"You can't hook the valve up backwards!"

Yes you most certainly can. Or are you saying it functions 100% the same even when backwards though? How do you know?

Thanks for the pics, I have them somewhere but that's handy!

[Andy4639]

The vacuum may be backwards but the valve doesn't care which way you mount it. It either opens when vacuum is applied are it closes when it's applied. So you need to know which way it operates. I guess we are saying the same thing in just different ways I think.

[davepl]

You believe they flow water backwards too when in the open position? There's no particular reason they shouldn't, but no reason they must either. Mine doesn't flow, so I presume the vacuum is wrong, but it was also backwards.

[Andy4639]

Originally Posted by davepl

You believe they flow water backwards too when in the open position? There's no particular reason they shouldn't, but no reason they must either. Mine doesn't flow, so I presume the vacuum is wrong, but it was also backwards.

When you say backwards your talking how it was mounted right? If so that shouldn't matter other than it's not mounted as it should be. that shouldn't effect the flow of the water. One of the lines need to be hooked to the water pump that would effect flow.

[Davidf]

maybe say it this way: water in/out direction does not matter. Some valves are normally open and some normally closed. I believe my '71 is normally open.

[davepl]

Yep, that's what I'm hearing. I still need to reverse it to have it in the "factory correct" orientation anyway.

I guess I'm saying "Prove it works backwards", but it's not really that important.

I figure unless someone has actually tried it, there's a chance it forces it shut when you try to flow backwards through it. If not, though, it's likely connected to the wrong port of the vacuum switch, and I'll go through the diagrams. Can't hurt to have both the water and vacuum plumbing "right" anyway.

[davepl]

Uh oh. The shop is saying my heater controls are bad, so I need to sort out what they're actually supposed to do.

In the diagrams posted above, you can see there's a 2-port control head where the water valve is CLOSED with vacuum applied.

The next one shows that there's a 3-port control head, which is what the reproduction I'm using has, and that the matching water valve is OPEN with vacuum applied.

I never noticed this difference until today. Since I would have ordered a 1970, and the Classic Industries catalog for 1969 shows a different unit, I expect I have the 1970 unit. It's the one pictured at the top of the thread.

Does anyone know, or have the time to check, where vacuum is present on the 2 ports of the 3-port control when its in the various settings (heat, ac freshair, ac recirc)? Then I could check to make sure it's working.

Does anyone also know if the pictured one is a "open with vacuum" or "closed with vacuum" design?