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Old 10-18-2012, 09:57 PM   #1
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AprilAire 700 wiring on old furnace???


Hi Folks.... longtime lurker, first time posting!

I just replaced an old wheel "sears" humidifier off my old Carrier Super Saver furnace that is nearly 25+ years old. Furnace is in good condition, but I wanted to replace the old humidifier. I picked up an AprilAire 700 and installed it just fine.... except that pesky wiring.

I'm looking for some help on what exactly to do.

I've got the supplied transformer wired to constant 120v power. The plug to the unit is also wired to constant 120v power. Now... where do all those colored wires go!! Any assistance would be much appreciated. Thanks for your time...

Here's the furnace control board:


Here's the transformer that I have installed:


Here's the humidstat automatic controller 700:

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Last edited by ryker99; 10-18-2012 at 10:15 PM.
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Old 10-19-2012, 06:16 AM   #2
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AprilAire 700 wiring on old furnace???




This is how it should be wired. I have left out the G and Gf connections because I believe that the humidifier should ONLY run with a call for heat.

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Old 10-19-2012, 06:16 AM   #3
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AprilAire 700 wiring on old furnace???


HH to the humidifier, R and C to the transformer you installed, C to furnace common, and W/G to the W terminal of the furnace.

The install manual should have all of this in it.
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Old 10-19-2012, 07:12 AM   #4
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AprilAire 700 wiring on old furnace???


Thanks for the help "beenthere" and "hvactech126". Looking at your responses, they don't seem to both align, unless I'm reading it totally wrong.

hvactech126 has R and C to humidstat, where beenthere has R and C to transformer....

When I ripped out my old sears humidifer, the EAC-1 and EAC-2 were both used, so looks like havactech126 makes the most sense based on previous wiring.

Thanks again for the help.
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Old 10-19-2012, 07:31 AM   #5
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AprilAire 700 wiring on old furnace???


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Originally Posted by hvactech126 View Post


This is how it should be wired. I have left out the G and Gf connections because I believe that the humidifier should ONLY run with a call for heat.
Okay... studying this diagram now... I've currently got transformer hooked up to constant 120v power. I need to remove that and install the transformer to the EAC-1 and EAC-2 on the board. Does it matter if black or white go to which EAC?
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Old 10-19-2012, 09:36 AM   #6
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AprilAire 700 wiring on old furnace???


You are correct. And no it does not matter which lead goes to each terminal.
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Old 10-19-2012, 10:55 AM   #7
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AprilAire 700 wiring on old furnace???


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Originally Posted by hvactech126 View Post
You are correct. And no it does not matter which lead goes to each terminal.
Okay. just hooked it up exactly as your diagram says and now I have no power to the transformer. So, either I smoked the board or the transformer during my frivolous wiring exercises the other day.
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Old 10-19-2012, 11:12 AM   #8
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AprilAire 700 wiring on old furnace???


The fan must be running in order for the transformer to be powered.
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Old 10-19-2012, 12:20 PM   #9
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AprilAire 700 wiring on old furnace???


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Originally Posted by hvactech126 View Post
The fan must be running in order for the transformer to be powered.
Okay. And if the humidstat isn't even powered on then it's a furnace board fail? The exhaust fan does work though on the furnace.
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Old 10-19-2012, 01:31 PM   #10
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AprilAire 700 wiring on old furnace???


To be operable to display humidity that digital humidistat needs to be powered with 24vac whether the furnace is running or not. I used an external plug-in 24vac transformer instead of hardwiring one for my Aprilaire 700.

The wiring diagram you are using is probably from one that used the old manual humidistat that did not require 24vac to operate and had no digital display. So if you want yours to display when the furnace is off you will need to either hardwire the xfmer to a constant 120v source or get a plug-in external like mine. Having said that I think it would still work OK like you have it, the stat just would be de-energized and have no readout when the furnace is off.
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Old 10-19-2012, 02:05 PM   #11
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AprilAire 700 wiring on old furnace???


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Originally Posted by raylo32 View Post
To be operable to display humidity that digital humidistat needs to be powered with 24vac whether the furnace is running or not. I used an external plug-in 24vac transformer instead of hardwiring one for my Aprilaire 700.

The wiring diagram you are using is probably from one that used the old manual humidistat that did not require 24vac to operate and had no digital display. So if you want yours to display when the furnace is off you will need to either hardwire the xfmer to a constant 120v source or get a plug-in external like mine. Having said that I think it would still work OK like you have it, the stat just would be de-energized and have no readout when the furnace is off.
Okay.... if I go back and wire in the thermostate to constant 120v source, what do I do with the EAC-1 and EAC-2 terminals on the furnace board?
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Old 10-19-2012, 02:18 PM   #12
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AprilAire 700 wiring on old furnace???


If you wired according to my diagram then the humidistat should be powered 24/7 from the R and C terminals on your control board in the furnace. The indoor blower must be running in order for the humidifier to actually run.
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Old 10-19-2012, 02:22 PM   #13
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AprilAire 700 wiring on old furnace???


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Originally Posted by hvactech126 View Post
If you wired according to my diagram then the humidistat should be powered 24/7 from the R and C terminals on your control board in the furnace. The indoor blower must be running in order for the humidifier to actually run.
I've done it exactly. What are thoughts on what is wrong? I do appreciate the continuous feedback!!
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Old 10-19-2012, 03:34 PM   #14
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AprilAire 700 wiring on old furnace???


Check for 24vac @ R and C on the furnace control board and at the humidistat.
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Old 10-19-2012, 04:22 PM   #15
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AprilAire 700 wiring on old furnace???


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Originally Posted by hvactech126 View Post
Check for 24vac @ R and C on the furnace control board and at the humidistat.
okay... 24v checked out perfect at board, transformer and humidstat.

Checked the EAC terminals and 0v. Blower did not turn on. We had ignition, flame and exhaust fan all worked.

So... now what??

Also, is there a way where I can wire for the humidstat to be constantly on? Humidstat turns on and off with furnace kick on.

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