Aprilaire 500A install, solenoid will not turn off

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Old 11-09-16, 06:07 PM
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Aprilaire 500A install, solenoid will not turn off

So I used this forum to install an Aprilaire 600M in our old house and everything went great. We recently built a new house and I wanted to install a whole house humidifier so I did some research and went with the Aprilaire 500A with the Aprilaire 60 digital humidistat.

Got everything installed and wired and when I put power back to the furnace the solenoid opened and started to supply water to the humidifier. This was with the humidistat off and the furnace not calling for heat or blower off. The only way I could get the solenoid to close was to unwire one of the wires from the transformer. With the solenoid unwired, I tested the humidifier in test mode and blower activation mode and everything worked besides solenoid control. I tired to troubleshoot this on my own for a while and then decided to call Aprilaire Tech support.

I walked thru my wiring with the support agent and he had me reset the humidistat. As I don't have a multi-meter at this point, he had me unwire both the "W" and "G" terminals from the humidistat and then touch the solenoid wire I had disconnected from the transformer back to the 24V. They state that if the solenoid did not open, I was getting feed thru from my wiring somewhere, if it did open, then the solenoid switch on the humidistat was bad and I needed a new one. I did the test and the solenoid opened. So I contacted the wholesaler I purchased the unit from and they sent me a new humidistat.

The new humidistat came today. I just swapped this out for the expected bad one and wired everything back up the same way. With the humidistat off and the furnace not calling for heat, when I supplied power back to the furnace the solenoid opened. I tried the same test as before and the solenoid opened. I can't believe that I got two bad humidistats and am now thinking that there is either something wrong with my wiring, or how I am supplying power to the transformer/solenoid.

Has anyone else ran into this or could someone review my install and let me know if I missed anything? Photos of my install are below

I powered the transformer from the switch that supplies power to the furnace. I brought this down to another junction box were it is wired to the transformer power supply lines.
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I then have the transformer wired to the humidistat and solenoid. Red is wired to one "H" terminal on humidistat and 10V on transformer. Blue is wired to one wire on solenoid.
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Here is my wiring for the solenoid. Blue goes to 24V on transformer. Yellow goes to other "H" terminal on humidistat
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Humidistat wiring photo below. Left red wire goes from "R" terminal on humidistat to the "R" terminal on furnace board. Left yellow wire goes from "C" terminal on humidistat to "C" terminal on furnace board. White wire goes from "W" terminal on humidistat to "W" terminal on furnace board. Green wire goes from "G" terminal on furnace board to green wire from humidistat. Right red wire is coming from the 10V side of transformer up to first "H" terminal on humidistat. Right yellow wire goes to solenoid valve. Blue wire goes from "Gf" terminal on humidistat to "G" terminal on furnace board.
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Furnace board wiring
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Overall install
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Any help is greatly appreciated!
 
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Old 11-09-16, 08:13 PM
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Welcome to the forums.

You mentioned 10v transformer several times.
Was that a mistake as the transformer should be 24vac ?

I don't use the G or Gf terminals when I install them as I don't allow the humidistat to run the humidifier without the heat as this is water wasteful and not very energy efficient as cold air doesn't carry humidity very well.

This is the diagram I always use and supply to the members here.....

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Old 11-10-16, 04:34 AM
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The transformer I have has 10VA and 24Vac stamped into it above the terminals. I tried to take a photo to show it. I changed the wiring around to your diagram and my solenoid is doing the same thing. Should I source power for the transformer from the HUM and NOM tabs on the furnace board instead of from the switch? The furnace is a Carrier.

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Old 11-10-16, 09:37 AM
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That is a 24vac 10 watt transformer and powering it where you have it connected is fine.

Blower activation mode should be off.
If you aren't using the ODT then the humidistat is run in manual mode.
Whenever switches are changed.... power needs to be removed and restored for changes to take effect.
 
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Old 11-11-16, 02:37 PM
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PJ,

Blower activation is off. I did hook up the ODT so the humidistat is in auto mode now. I reset the humidistat by removing the red wire from the "R" terminal to remove power and reset it.

After doing all that solenoid is still open and not being controlled via humidifier.
 
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