Question about Aprilaire 600 Humidifier

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Solenoid won't open--voltage drops when connected to humidistat

Our Aprilaire 600 humidifier's solenoid doesn't open, so no water ever goes through.  I think I've isolated the problem to the solenoid itself.  The humidistat is providing the right voltage to the solenoid when the heater is on and blowing heat (I verified this by disconnecting the humidistat's wires from the yellow solenoid wires and used a multimeter--showed 24V).  But when I connect the wires back to the solenoid, and go through the same process, it only shows 0.1V, and the solenoid doesn't click or open. So it seems the solenoid is messing with the voltage?
My humidistat is set to manual, and I've verified the voltage as well at the humidistat H terminals and found the same results (24V when not connected to the solenoid and heater on, 0.1V when connected and heater on).  On a side note, the humidistat clicks but the solenoid never does.  
Any ideas what to test next?  Everything else in the chain is working (checked filter, saddle valve, and blew through top part to make sure there were no obstructions--there weren't).

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The coil may shorting out the 24vac supply to the solenoid. Recommend replacing soleniod.
Normally you should be able to read the 24vac across the solenoid when energized.
The other option is to get a 120vac to 24vac transformer and test the solenoid. This way you will know if the solenoid is the cause or the 24vac source is the problem.

Posted on Mar 10, 2009

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