Need help with Aprilaire 400M Humidifier, cannot open Saddle valve for water

[mtlmonk]

Hello,

I have an Aprilaire 400M humidifier.

Cannot find a way to open up the saddle valve to let water run.

I took my parts (overflow part at the bottom and saddle valve) and installed in my neighbor's setup (he has the same model) and it worked no problem.

I have the same wiring setup as him also.

From furnace, took White wire and plugged to yellow of valve.
Other Yellow of valve, into White of Overflow part
Other White of Overflow part into Black wire from furnace

In other words, Furnace -> Valve, Valve -> Overflow part, Overflow part to Furnace (-> is a wire)

With a voltmeter, I have checked that current is passed to the valve.

When the humidistat is off, it sends 12V to the valve but whenever humidistat is on, it becomes 0 on the valve.

I have tested current coming out of the furnace when setting the humidistat to On, without plugging to the valve, and it's around 24V.

What is wrong?  

[Admin]

You probably have a faulty water level sensor (overflow part).

Disconnect both water level sensor wires (white wires).  That should leave you with a free yellow solenoid wire and a free black furnace wire.  Connect the yellow and black wires together.

Now turn the power back on and test the system.  The solenoid should open once the humidistat gets powered and is turned on.  The humidistat might only get powered when the furnace is heating.

If your humidifier has a drain line connected to the bottom I would remove the water level sensor assembly entirely and use that humidifier without it.  It would operate like the Aprilaire 500 model.