I can't get this humidistat to work with an AprilAire 550! The manual says "can be used with most humidifiers." I'm assuming they mean any 24V humidifier and not a 120V type.

I scanned the wire diagram...If you follow this link, you can see it:

Instead of using the W terminal like in the diagram, I want to use a transformer that will be engergized by the HUM terminal on the furnace. This way, it can humidify with heat or fan mode. The power to energize the humidistat display will come from the Tstat like in the diagram,

The problem is that I'm always always getting voltage at the H1 terminal on the humidistat. If I cycle it on or off, there's always 24V.

What am I missing?