Troubleshooting AprilAire Humidifier

I think I screwed something up.



I have an AprilAire humidifier which is mounted on the return side of our air handler. It hasn't worked in a while, and I'm not sure when it stopped working. But the symptom now is that the solenoid value clicks open, then immediately shuts. I replaced the solenoid valve. Same thing happens. If I turned the humidity setting down, then back up, the valve again opens then immediately closes.



So I took the humidistat out of the circuit and just shorted the leads together with a test lead with alligator clips on each end. Again the valve opens then immediately shuts. If I open the circuit and close it again, the valve again cycles.



I'm beginning to wonder if I dorked something up when I swapped out the fan motor. It's a two-speed fan, and it functions fine (high speed when the heat pump is running, low speed when on electric strips alone).



The 24VAC for the humidifier comes off a device that wired into the fan control. I'm assuming all it does is sense whether the fan is running, and it so, passes the 24VAC on to the humidifier.



Does this sound like that device is bad? I can't think what else it would be - there's nothing else in the humidifier control circuit, and the system otherwise runs fine.



Thanks.