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

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.