Humidifier solenoid works -- unless it's hooked up to the furnace

11 years ago

I have a one year old Aprilaire humidifier. This season we found the water wasn't running.

To troubleshoot I disconnected the solenoid (a #4040) and hooked it directly to a transformer. The solenoid then opens. The transformer is reading 21.8 VAC.

However, when I hook the solenoid up to the furnace and crank everything up, the solenoid won't open. I'm getting a reading of 26.9 VAC from the furnace.

If the solenoid just never opened up the solution would be simple -- try cleaning or replace the solenoid. But this has me perplexed. Any thoughts?

-Dennis

Comments (8)

mike_home
11 years ago
How can the voltage be 26.9V at the furnace and only 21.8V at the transformer? Are you sure your measurements are correct?
hennen
Original Author
11 years ago
I'm certain the measurements are correct. I took them many times to make sure.

The transformer I'm testing against is the doorbell transformer. The measurement at the solenoid is the wires that would hook up directly to the solenoid coming from the furnace and humidistat.
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mike_home
11 years ago
I misunderstood your original post. I thought your were testing with the furnace transformer.

Are you reading 26.9V when the furnace is running and the humidifier is trying to run? If that is true then it doesn't seem to be a low voltage problem.

Does your meter measure AC current? If it does then set the meter to current measurement and connect in series on one of the wires between the solenoid and the humidifier control. The current should go from zero to some value when you turn on the humidifier. If it does not, then you have an open circuit. The humidifier control board may need to be replaced.
hennen
Original Author
11 years ago
Yes, the 26.9V reading is when the furnace is running and calling for humidity.

Setting the meter to mA AC and putting it in series while everything is running gives no current.

So it sounds like the solenoid is probably okay and I need to call in?
mike_home
11 years ago
If the solenoid opens when connected to the bell transformer then I would agree it is good. If you want to convince yourself measure the current when you hook it up to the bell transformer. I would think you would see at least 0.5 amps.

The switch inside the humidifier is probably bad. You you may need to replace the control board. You may be covered under the warranty for at least the parts.
countryboymo
11 years ago
I added a transformer inside the furnace solely for the humidifier solenoid because I had a solenoid short out and burn the board on the furnace. The solenoid was the ultimate culprit but at least if this one fails it will just take out a fuse and not a whole board.
hennen
Original Author
11 years ago
It was in fact the humidistat.

I took it out and by-passed it and the solenoid now opens.

It was probably the cheapest thing the builder could find, so I'm going to take the opportunity to replace it with something a little better.

Thanks for your help!
countryboymo
11 years ago
I had that setup and had horrible swings in humidity from rain forest to arizona cactus. I upgraded to a stat that controls humidity and also has frost protection so as the temp drops it lets the humidity drop a little to keep the windows from sweating which is only an issue if it gets below zero here. If I had old windows I could adjust the frost protection to be more active or just turn it off.

Humidifier solenoid works -- unless it's hooked up to the furnace

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Humidifier solenoid works -- unless it's hooked up to the furnace

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