This is the controller that sends vacuum to the door in the snorkel that adjusts the mixture of ambient and warmed air being pulled into the air cleaner. Mine leaks vacuum. The 1974 parts catalog lists part number 3514168, but I see many similar-looking parts available at widely varying prices. Some have a numbering system like ATS9, ATS10, etc.

1. How do they work?
2. Are these all the same if they look the same, or do they have different internal calibrated parts?
3. If they are different, which is best for my engine?
4. If the vacuum leak doesn't noticeably affect idle RPM or manifold vacuum, and the snorkel door opens and closes, does a small vacuum leak even matter?

Concerning your existing part. I would rig up a bench test using a vacuum pump with a gauge and maybe a hot plate / toaster oven and a non contact thermometer and verify that it is working over time or not in a stable and consistent manner across the temperatures and vacuum signals that are expected.
If it is, your replacement part search maybe over. If it is not,,, I would buy one or more across the counter from a source where I could return it or exchange it and the run the bench tests to see how the replacement part(s) compares.

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Chrysler and Ford used the metal "flying saucer" type sensor made by Fram. That would be one like this. I prefer the GM/AMC AC-type sensors, which are less prone to dust grains blocking them partly open, and they're faster to react to air temperature because of their open-frame design. They retrofit easily; you just have to slightly ovalise one or both of the holes in the air cleaner base because the two vacuum nipples are spaced very slightly differently. That would be one like this.

There are different temperature calibrations—many of them. They mattered when the cars were being squeaked past their emissions type-approval tests so the automakers would be allowed to offer them for sale. The calibration differences are much less important after those type-approval tests have been passed, so don't fret or sweat exact part numbers. Also note that under certain conditions it can be normal to feel a very small(!) amount of vacuum at the open port on top of the sensor. If there's more than that, occasionally you can get lucky by spraying a bit of carb cleaner in that open port with the engine running; if there's dirt on the valve seat that sometimes flushes it out—but don't count on it.

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