C-wire for Wifi thermostat with Aprilaire humidifier

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Old 12-28-15, 01:17 PM
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C-wire for Wifi thermostat with Aprilaire humidifier

I'm trying to install a Honeywell RTH6580WF Wifi Thermostat, but I do not currently have a C-Wire at the old thermostat (see first picture). My plan has been to do the G-wire substitution.

However, there are two wires attached to the C-terminal at the furnace block (see second picture). I'm guessing those wires are related to the Aprilaire 600 Humidifer that I had someone install last year.

So, two questions:

(1) Will the G-wire substitution mess up my Aprilaire humidifier?

(2) If not, do I simply move the G-wire to the C-terminal at the furnace, even though there are already two wires there?

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Old 12-28-15, 01:29 PM
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Welcome to the forums.

Try removing the old thermostat backing plate from the wall. Then see if you can pull a little more thermostat wire from the wall opening. If you are lucky, you will find the blue "C" wire tucked in the wall if it was not needed with the original thermostat.
 
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Old 12-28-15, 02:45 PM
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goldstar,

I already looked back there. All four of those wires are wrapped in a single sheath. I don't see any other wires down in there.

I'm guessing the wire(s) at the C-terminal of the furnace were put in recently with the Aprilaire humidifier.
 
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Old 12-28-15, 04:51 PM
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You should be able to connect green to C at both ends without any problems if you have a gas furnace.

3 wires on C is fine.

Add a jumper from Y to G at the furnace.
 
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Old 12-28-15, 04:58 PM
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The picture illustrates the new wiring. Be careful to leave the existing wires on their respective terminals. You will move the green wire from G to C. You will add a jumper from G to Y.

At the stat end..... the green wire will now be your C wire.

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Be sure the power is off before making any wiring changes and until the install is done.
 
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Old 01-02-16, 10:37 AM
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I changed the wiring, plugged it in, and it worked. But after I unplugged the thermostat to attach it permanently to the wall and re-plugged it in, now it's not getting power.

My aprilaire humidifer (also plugged into the c terminal) is not getting power either.

What happened? Is it possible that I overloaded the c terminal and blew something?

Please respond ASAP! I don't have heat until I fix this!
 
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Old 01-02-16, 10:48 AM
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Check for an automotive type plastic fuse on the control board. It will be 3A or 5A.
 
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Old 01-02-16, 11:09 AM
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I found the fuse. It looks blown. Is this fuse the same as ones used in car? Could I grab an extra 5 amp fuse from my car to test it?
 
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Old 01-02-16, 11:20 AM
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Yes.... and yes. You may have shorted the wiring at the stat when putting the stat back on.
 
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Old 01-02-16, 11:23 AM
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If I shorted the wire does that mean a new fuse won't fix it?
 
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Old 01-02-16, 11:51 AM
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Ok, I got a new fuse in there and it's running. However, for the moment I have the humidifier turned off. We'll see if the fuse blows again when I turn the humidifer on and both the thermostat and humidifer are drawing power.
 
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Old 01-02-16, 12:00 PM
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If the fuse was black where the link is..... you created a short.
If the fuse was just open.... it was overloaded.

You said you had the stat off the wall and then you reattached it. That is most likely when the fuse blew.
 
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Old 12-07-16, 08:00 PM
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24V AC Transformer for Aprilaire Humidistat

Your help would be appreciated:

I did a G-to-C wire substitution to power a new Wifi thermostat. My Aprilaire 600 humidifier (just the humidistat?) is apparently getting power from the same source. When I run both at the same time, the 5A fuse blows on the furnace board.

See details here from when I asked about this on the forum.

My question now: Can I run the humidistat from a 24V transformer (this one) plugged in to a wall outlet? And if so, will it fix my problem because the humidifier and thermostat are getting power from separate sources?

Thanks!
 
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Old 12-07-16, 08:13 PM
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Welcome back. You'll notice I combined your two threads. Two much pertinent info in the first one.

You will move the green wire from G to C. You will add a jumper from G to Y
You misread the info.

Think of every stat letter as a 24vac positive and the C is negative.
There really isn't positive or negative... just used as an analogy.

So.... a jumper between G and C is a direct short.

Now we need to see what you've got for wiring. You shouldn't need a second transformer.
You have a 600A humidifier. Are you using the electronic humidistat ?
 
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Old 12-07-16, 08:20 PM
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Thanks for responding quickly.

Pretty sure I did it as instructed. Jumper between G and Y, not G and C.

For whatever reason, powering on the humidifier and the thermostat at the same time blows the 5A fuse. So I'm wondering if a wall-outlet 24V transformer can be used to power the humidistat instead of getting power from the furnace.

I'll take some pictures.
 
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Old 12-07-16, 08:30 PM
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Here is the new wiring at the furnace:

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Old 12-07-16, 08:34 PM
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Here is the Humidistat:

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Old 12-07-16, 08:35 PM
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It's not due to over current. I believe you have a wiring issue.

Just FYI..... at your furnace control board you have three cables.

One cable is the thermostat..... red, white, blue and green
One cable is the A/C condensor..... red and white
One cable is the humidifier.... light blue, dark blue and red.

Am I right..... I can't see the actual cables.

Ahhhh.... snuck the pics in....cool. Pull the cover off the hstat and repost it.

What is that transformer in the bottom left for..... the humidifier ??
Is it live all the time ?
 
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Old 12-07-16, 08:51 PM
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About to post more pictures.
 
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Old 12-07-16, 08:57 PM
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Cable going to thermostat = red, white, blue and green

(Same as you said)

Cable going to A/C condensor = red, white and light blue

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Cable going to humidifier = dark blue, green, red and white and yellow

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Old 12-07-16, 09:04 PM
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In addition to the humidifier cable, there are also wires spliced from the A/C condensor cable going to the humidifier. (Maybe this would be more related to activating the blower than about powering the unit?) See photo:

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Then this is my description of the humidistat unit:

1. The dark brown wire is cable going directly from furnace to the humidifier.
2. The light brown cable from the right was spliced from the A/C condenser cable.
3. The light brown cable on the left is headed to the humidifier unit.

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Old 12-07-16, 09:13 PM
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What is that transformer in the bottom left for..... the humidifier ??
Looks like it's for the humidifier. Assuming the larger black and white wires are just the 110V power source, all of the smaller wires go to the humidifier.

Is it live all the time ?
Not sure. How would I know? Right now the thermostat is powered off.
 
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Old 12-07-16, 09:31 PM
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Wow... what a mess. Looks like you inherited a science project. Now people know why it costs money to have this stuff fixed.

The wiring here is easy in itself. It's the splices that make it hard.

The transformer is used to power the humidifier solenoid only. That's good.
The wiring spliced into the A/C condensor line.... light blue and green are the wires for the outdoor temperature sensor for the automatic humidistat. If you were to check out in A/C condensor..... you'd find a little sensor connected to those two wires.

Let me look over the pics and I'll respond around 1:00 eastern.
 
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Old 12-07-16, 10:15 PM
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Remove the brown wire from the G terminal and cap off.
Remove the green from the Gf terminal and cap off.

Several issues at the furnace. At the furnace.....

Remove the green wire from C and cap it off. This green wire goes to the humidistat and doesn't belong there. Look at the picture..... you are using the wrong green wire for C.
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The green from the four wire thermostat cable belongs on C at furnace. The green stat wire may connect to brown now. If it does...... disconnect it from brown, cap brown off and connect the green to C.


Just FYI...............
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The confusion with the greens is because the humidistat was wired for fan control. We've now removed that.
 
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Old 12-08-16, 07:20 AM
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First, I want to thank you sincerely for the time you've put into helping me.

The confusion with the greens is because the humidistat was wired for fan control. We've now removed that.
I think that was on purpose so that the humidifier could run when the furnace is not. With your proposed change, would that mean the humidifier will only run when the furnace is running?

Remove the brown wire from the G terminal and cap off.
Remove the green from the Gf terminal and cap off.
This is clear.

Remove the green wire from C and cap it off. (Then later The green from the four wire thermostat cable belongs on C at furnace.
Seems like you're saying the green does not belong on C and then that it does belong on C. Can you clarify?

The green stat wire may connect to brown now. If it does...... disconnect it from brown, cap brown off and connect the green to C.
Sorry, I don't know you mean by "the green stat wire may connect to brown now."

Thanks for all your help!!
 
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Old 12-09-16, 07:59 PM
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Pete, can you clarify this for me? I'm going to tackle this tomorrow.

Thanks!
 
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Old 01-21-17, 12:11 PM
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<bump>

Is Pete still around to clarify this? Anyone else? (see request for clarification on Pete's most recent instructions)

I'm stuck and would like to get this taken care of.

Thanks!
 
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Old 01-21-17, 12:28 PM
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How did I miss this. My bad.

Wow... I have to go back and reread the thread to get my train of thought back.
 
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