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Discussion Starter · #1 ·
Hi all...great forum here. I had a question for the experts here and i am not to versed in the one area around the connection the solenoid valve.

My existing whole house humidifier took a dive this week and replacing it has not been that difficult for the most part. It replaced it with an AprilAire 500 automatic hooked up to my existing Trane XV95 furnace. I ran the outdoor sensor as well.

My issue is i don't quite know how to power the solenoid valve. I read that i requires a 24v constant connection with 1 wire powered and the other into the Model 60 humidistat. The unit came with a transformer box but i was wondering if i could just power the valve with one of the existing outlets on my furnace board. I posted a few pics below. Thanks in advance!!
 

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It's common to use power from the board to run the solenoid. That comes from the C and R terminals. Run either leg through the humidistat switch.

If you didn't have the automatic unit, you'd connect to the C and W on the board. I see a connection there now so your old usit wasn't automatic, I guess.

I think that board also has dry switching contacts (or possibly powered) for humidifiers. Your way is also good so not to worry about changing it to use that but if curious, measure the output on the H and H or U and U terminals during heat call mode, whichever it may have. Standards are 120 vac, 24 vac and dry switch (closes on heat mode).
 

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Yes, you should only have to supply the C and R leg in the loop for the solenoid if you have the automatic model. Double check the diagram thatcame with it and make sure you have it wired right.
 

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Backing up here, You may have to use the W connection instead of the R. It depends on which control you have. There are three different ones and 6 ways to wire them so it gets a little dicey at times. Using the W leg has always been the easiest way to go with the manual control but there are 2 different automatic controls, one has a digital readout and the other doesn't.

Give me the model of the control you are using and I'll see if I can find the correct schematic for you.
 

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Discussion Starter · #6 ·
Backing up here, You may have to use the W connection instead of the R. It depends on which control you have. There are three different ones and 6 ways to wire them so it gets a little dicey at times. Using the W leg has always been the easiest way to go with the manual control but there are 2 different automatic controls, one has a digital readout and the other doesn't.

Give me the model of the control you are using and I'll see if I can find the correct schematic for you.
Yeah..i treid the R wire and i didn't hear the valve click open. I have the Aprilaire Model 60 (digital readout version).

Looking at the pic above, W1 has 2 wires in it. Can you use the W2 terminal? Let me know what you think. Moving the wires are not hard :) Thanks for the help!
 

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That's digital control is a different animal. Give me a moment and I'll see if I can get the schematic for it.

I also need to know what kind of thermostat you are using.... is it a digital or mechanical. Model number will help if you aren't sure.
 

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OK... Nest thermostat.. I'll see what I can find.
 

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As expected, AprilAire doesn't have a schematic posted for using the AA 500 and Digital Control with a Nest system. All of their schematics are assuming a mechanical thermostat. We'll have to wing it.

Here's how we start:

From your
Humidistat Control
R terminal -----------------> to R on furnace
C ---------------------------> to B/C on furnace
ODT------------------------> to outdoor temperature sensor
ODT------------------------> to outdoor temperature sensor
W --------------------------> to W on furnace
G --------------------------> no connection (I don't think needed with Nest system)
H --------------------------> to humidifier (brown wire) solenoid
H --------------------------> to humidifier (brown wire) solenoid
Gf--------------------------> to G on furnace
 

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When you finish the wiring as outlined, turn on the power and check that the control display works as far as readout is concerned. Turn the humidistat knob down and up and listen to hear if the solenoid clicks. I don't expect it to at this stage of the wiring since I'm winging it in the safest mode possible. I suspect the H terminals are dry switch type but I'm not going to assume that until it's proven that the solenoid doesn't work as wired.

If everything works except the solenoid doesn't get any voltage, we will address that and affect an easy fix.
 

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Use the transformer that came with the humidifier. That way, if the humidifier shorts out, you don't lose your heat also.

If you intend to have the humidifier work in fan on mode, then you have to connect the humidifier to the G terminal of the furnace also.
 

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Discussion Starter · #13 ·
Thanks for the info. I think i may just go the transformer route. At this point, everything is working except the opening of the solennoid valve.
 

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OK, sounds like we got what was expected... that's good. I had to do it that way to make sure that those H output screws weren't powered.
Now it's up to you how you want to supply the 24 vac into the loop serving the solenoid.

You can use the transformer provided with the humidifier if you like. Then run a wire from it to the humidifier and insert it in the solenoid loop. That requires some line voltage work on your part... be careful. AprilAire says not to mount it inside the furnace. They suggest having it arrached to a junction box outside the furnace that can have the furnace power feed wires in and connecting the transformer to that circuit. I suspect they don't want to risk the liability of instructing you to alter the furnace wiring. I won't advise diferently although it's usually put in the furnace.

Otherwise, you can use the 24 vac that already there on that terminal strip at the R and C terminals. The solenoid only pulls .08 amps (80 milliamps). That method would require a 2 conductor wire approx. 8" long.

If you need further, post back.
 

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Discussion Starter · #15 ·
OK, sounds like we got what was expected... that's good. I had to do it that way to make sure that those H output screws weren't powered.
Now it's up to you how you want to supply the 24 vac into the loop serving the solenoid.

You can use the transformer provided with the humidifier if you like. Then run a wire from it to the humidifier and insert it in the solenoid loop. That requires some line voltage work on your part... be careful. AprilAire says not to mount it inside the furnace. They suggest having it arrached to a junction box outside the furnace that can have the furnace power feed wires in and connecting the transformer to that circuit. I suspect they don't want to risk the liability of instructing you to alter the furnace wiring. I won't advise diferently although it's usually put in the furnace.

Otherwise, you can use the 24 vac that already there on that terminal strip at the R and C terminals. The solenoid only pulls .08 amps (80 milliamps). That method would require a 2 conductor wire approx. 8" long.

If you need further, post back.
So you are saying that i can run a wire from the R or C and just use that as my 24 v feed? I'd prefer to do that if that would would work.
 

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So you are saying that i can run a wire from the R or C and just use that as my 24 v feed? I'd prefer to do that if that would would work.
That's correct. Run it over and connect in series with the solenoid loop. That's just as reliable as having a separate transformer. Good engineering says use as few components as possible unless you need redundancy for life safety.

Generally that transformer is used when the manual thermostat is used with a furnace that has no control board outputs for a humidifier and the current sensing switch has to be used. You don't need to go out of your way to use it. :wink2:
 

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That's correct. Run it over and connect in series with the solenoid loop. That's just as reliable as having a separate transformer. Good engineering says use as few components as possible unless you need redundancy for life safety.

Generally that transformer is used when the manual thermostat is used with a furnace that has no control board outputs for a humidifier and the current sensing switch has to be used. You don't need to go out of your way to use it. :wink2:

Generally, that transformer is used to protect the furnace.
 
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