From what I recall the control on the dash varies the bimetal strip that then changes the vacuum flow. When hot air passes over the bimetal strip it moves the pin to close the small orifice which reduces the vacuum flow. That is how it regulates the vacuum and how much the vacuum controlled intake manifold valve is open. 
If you can't get any movement of air through it when sucking on the line then I would suspect the pin is seized shut like mine was, and the rubber diaphragm is probably good. If the diaphragm was faulty then air would leak when blocking the other vacuum outlet.
 As mentioned it has been a long time and I'm doing this from sometimes faulty memory.

My 54 has the heater type that has three hoses as mentioned above.  The 56 Bird has the two hose system, valve on intake and the valve (cricket) in the heater box.  The bird system gave me problems, so I went with the CASCO kit which has a manual control using the stock dash controls.  This kit works pretty good  -  but the temp is harder to control in my opinion.


54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

I did not know about the two types of heater systems. I just work on the one I have. I did add a vacuum control valve on the engine though. Had a problem in a cold winter with my 57. Did an engine change outside in December in Missouri. COLD and after my heater didn't work. I spent the whole winter freezing. I checked the temp control cable at the heater and everything appeared to work correctly. In the early spring I was working under the hood and heard a hissing sound. Found a vacuum hose off the back of the intake not connected so I plugged it in. When i got back in the car to move it it was HOT inside. Didn't relize that the cable didn't actually open the valve it just allowed the vacuum to open it. I always had to learn the hard way. Still do I think.

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

I had that System on the 56 I had for Years. I believe there actually 3 Hoses that go into the Firewall Hookups. This System on mine now has the Vacuum Control Valve on the Intake and the Temperature is controlled by this Cricket Valve I am trying to get working. I don't think the System You have is even covered in the Shop Manual. I believe its referred to as the "recirculating"Heater. No Rhyme or reason why they were installed in some Cars and not Others. No Mention that it was offered in the Brochure or the Accessories Manual.

  

That was a spell check error I typed lever. Referring to the temp control slider that attaches to the valve.

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

I think some of the confusion comes from the 56 cars having 2 entirely different heater control systems,   Mine has a firewall mount valve in series with the heater hoses, the back side of the valve is under the dash and has a cable controlled bu the hot-cold lever on the control panel, I think it also has a capillary temp sensor in the heater box to automatically regulate temperature.

The other type has a vacuum controlled valve on the intake manifold that connects to the heater hose supplying the heater core, the vacuum source is a valve (I am assuming temperature sensitive) in the heater box to control how much vacuum is supplied to the manifold valve thereby controlling the air temperature.


I have no idea what system the Birds or 55 cars used.

Are You referring to my original  Question or? Not sure what You mean about "Dash Level hooked to it"?  Vacuum Line from Manifold to the Valve and line out to Valve on Intake Manifold. The Heat Control on high which opens the Valve on Heater. There is nothing coming through the Valve to the Valve on Intake Manifold. I assume there should be vacuum coming through?

  

Those darn little tabs rarely all go back. Just a odd question but have you got the dash level hooked to it? Ask me at Edgewater and I'll tell you about my experience with these little valves. You said that the vacuum is leaking through so I expect it is the diaphragm just wanted to throw in my 2 bits.

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

It becomes obvious when you open it up. It has been a while but from what I remember real the only fiddly bit was crimping it back together. I think one of the tabs broke off and I had to solder it back on.

If you (or anyone else here) can find another to experiment with, take it apart & replace with "raw" diaphragm material that you'd custom-cut for the application  -  that "stuff" has to be "out there", and available as raw material.

Otherwise, I'd be willing to "take a crack at it" if someone can provide an old one on which to experiment.  The only one I have presently is a "spare" good one; on which I am not willing to work.

Contact me through PM if you have one to send for experimentation (even one from which the temp. sense coil is broken-off; just need the basic valve to see how it comes apart and is built inside).

Thanks, JLB




55 Ford Crown Victoria Steel Top