I too, am puzzled, in regard to the Ampico that does not play, _but_
(you say) the soft and sustain pedals _do_ operate.  This indicates
that the pump pressure is high enough to operate the pedal pneumatics.

This is odd, because the supply for the pedal pneumatics comes from the
same source as that of each side of the stack.  The cut-out pouch, also
cuts out the pedal pneumatics.  According to that, the cut-out pouch is
working properly.  If there were tremendous leaks in the valves for the
striker pneumatics, there would not be enough vacuum to operate the
pedal pneumatics.

Bob Lemon suggested that the nipples on the pump distribution and
action cut-off block may have been driven in too far.  If these nipples
are driven too far, they do not contact solid wood.( at least in any
Ampico distribution box I have examined) the large nipples would only
be partially blocked and not enough to silence the pneumatic stack.

Have you tried gently lifting the rod for the expression, to be certain
that something is not pushing downward on them, or they are not stuck
in any way?

Were the unit valves rebuilt using neoprene?  If so, they can ooze
sticky goo, that will seal them shut.

Have you had any pranksters visiting you?

Years ago, we played a trick on Larry Mangus.  He had just rebuilt
a beautiful Model B Ampico.  On April Fools Day we took a piece of
transparent tape and neatly covered his tracker bar.  Larry came into
the room to demonstrate his newest restoration, and of course it did
nothing.

We had quite a time to keep from laughing.  Larry did not have much of
a sense of humor when a joke was played on him!

Bruce Clark