I have an AprilAire. It seems that when I turn the humidistat to the point
of right where it clicks on, the humidifier runs with each and every furnace
cycle. If I turn it until it just clicks off, it never runs with any
furnace cycle.

I guess I would expect that setting it right at the brink would make the
humidifier run occasionally. But my house goes from either being a desert,
to having moss and ferns growing on the walls.

Should it behave like this, or do I need to replace the humidistat? I would
be interested in hearing from other AprilAire owners.

I have the model that sits on the cold-air return side. The humidistat is
also on the cold-air return duct. Maybe that's part of the problem. Maybe
it should be on the hot side.