The valve has a vacuam hose to it from where?I think it goes thru the firewall to a vac port under the dash? Is that correct?
This is on my 72 Elcam 402. http://www.chevelles.com/forum/biggrin.gif
It shuts off the water to the heater while the AC is on.
Rick

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66 300 Deluxe 350/330hp
71 350 malibu (project car)
72 Elcam 402SS
78 Malibu Classic (daily driver)

It goes to a vacuum control on the heater control assembly. There are two vacuum controls, it is the one that is hooked to the temp lever. Philip

Thanks Pilip, I've seen some 70-72s with a little vacuam pod mounted on the AC/heater box and then some don't.I seem to remember my 71 from years ago had one but my 71 now doesn't,what's it for???
Rick


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66 300 Deluxe 350/330hp
71 350 malibu (project car)
72 Elcam 402SS
78 Malibu Classic (daily driver)

This is a vacuumn resevoir for the heat/ac system to move the air duct doors.

The purpose of the vacuum reservoir was to keep the heat/AC from changing under low vaccum conditions, like wide open throttle and when pulling hills. Someone has probably removed it.

I have read in earlier posts that '70 was the last year for the vacuum operated water valve. After that, there is no valve in the system. The 1972 factory assembly manual shows no valve for the heater hoses. I have 2 '72 models which are pretty original and neither has a water valve. Probably someone has added that valve from an earlier car.

Sorry JW but the valve on 71-72 BB is on the intake manifold. Looks like an upside down L. Now on a small block I am not sure if they had one or not. But the reason you might be missing them JW is that often these broke, rusted or were taken out when work was done on the car. It's basically in the way if you need to work on the valvetrain on the passenger side. Not gospel but just what I have noticed and read up on when we did our 71.

J.J. Fig

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MCC member #256
http://www.clark.net/pub/chevelle/mcc.htm

JW,my 71 project car has one (valve) in the intake but no vac.canister and there isn't any screw holes in the housing as if there was one.This car seems to be very original
and rusted.THe vac.pod was mounted on the corner of the ac housing with 2 screws.
If I reinstall the valve in the new manifold where does the vacuam line enter the firewall?Up on the firewall, next to the ac dog house is a little vacuam diaghram with vac.from the intake manifold and is clamped to the firewall and ac dog house.It's other end runs thru the firewall to ???? I presume to the heater controls????
Thanks guys for all the info. http://www.chevelles.com/forum/biggrin.gif http://www.chevelles.com/forum/biggrin.gif
Rick

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66 300 Deluxe 350/330hp
71 350 malibu (project car)
72 Elcam 402SS
78 Malibu Classic (daily driver)

Fig: I am familiar with that type of valve. The assembly manual illustrations show the hose going right onto the manifold. That valve would be big enough to show up pretty well, I would think.
I found pages for general hose routings and pages for refrigerant and heater hose routings.Also there is info on the vacuum hose routings. None of these show a vacuum operated shutoff valve.
In the shop manual there are diagrams of the vacuum system for the AC system and it shows no provision for a water shut off valve.The text of the manual states:"Since the unit has no water valve, water circulation keeps the core hot at all times." I done my best... Beats me.

[This message has been edited by JWagner (edited 03-08-2000).]