Karen,

I do not have the precise vacuum, but I imagine that Amel probably adjusts the vacuum switch when it is installed. Here is the information I have in my book. The source of this information was Amel:

The Amel Sea Chest has an Amel innovative Vacuum Switch attached
via a hose to the Sea Chest Manifold. The Vacuum Switch is located
above the sea chest. Sea Chest blockage will create suction inside the
Sea Chest, which closes the switch, activating an alarm. Test this alarm
switch by closing the Sea Chest valve for up to 8 seconds while the engine
is running.

The internal part of the switch can get clogged as well as the curved
copper pipe. If the alarm isn't working, check for clogs.
To adjust the sensitivity of the vacuum switch, remove the top screw, then
using a jeweler's flat head screwdriver, inserted into a tiny, concealed
adjuster screw adjust the sensitivity. Turning the small screw clockwise,
increases sensitivity and the alarm comes on. Anticlockwise and the alarm
stops. Through trial and error, you will find the ‘sweet spot’ by running
the fridges, AC, engine, and generator at the same time. NOTE:
Adjusting sensitivity doesn't require the removal of the Vacuum Switch.