Hooking up Honeywell 8908 Humidistat to Trane Whole Home...

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Old 12-09-15, 08:09 PM
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Hooking up Honeywell 8908 Humidistat to Trane Whole Home...

Hello,

We purchased a home around a year ago and I noticed that the whole-home humidifier is not working (does not seem to be kicking on, no water flow). Anyhow, I had it serviced and the tech said the humidistat was bad and wanted to charge $350 to replace it, which I thought was nuts.

So, I picked up a manual one, the Honeywell 8908, which I think should work just fine. My current one humidistat (from Trane, the original to the system) is hooked up to an outdoor sensor which I am assuming I can live without?

I assume it would be an easy job but I am a little confused on the wiring. My broken Trane humidistat was three wires going into it: 24 AC, A/A, and the Outdoor Sensor.

I know the 24 AC is power, but what is A/A? Also, both the 24 AC and A/A have a black and red wire.

Now, the new Honeywell only has 2 connections and I am not sure what goes where, since they are not well marked. Can anyone give me a tip as to what goes where? Do I need both red and black wires? Obviously, 24 AC goes somewhere, but what about A/A?

Thank you!!
 
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Old 12-09-15, 10:39 PM
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A/A is the wiring to the humidifier.

Do you know which humidifier you have..... does it have an AC plug attached to it ?
The link has the models.....
TRANE humidifier store/thumd500_product_data.pdf
 
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Old 12-10-15, 04:00 AM
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The Trane is a 300A. I do not see or notice any AC plug. Thanks!
 
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Old 12-10-15, 07:40 AM
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Thank you the diagram -- it does make a little more sense now with using the manual humidistat. I am just not sure since the 24 AC and A/A each have two wires (red and black) and the new one I have only has two, and they don't seem to be labeled. I would assume I don't want to mix the red and blacks, but maybe I only use one color? I want the humidifier to kick on with just the heat, like it used to. Thank you for any advice!
 
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Old 12-10-15, 09:20 AM
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Since you're working with 24v AC..... there is no polarity. You can connect red to red or red to black. You just want to end up with a series circuit. In the diagram below is how I would connect it.

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Old 12-10-15, 11:25 AM
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Thank you! I am not quite sure what you mean by series circuit. Currently I have a red/black going to 24 AC and a red/back going to A/A.

Do I just combine both colors for 24 AC and connect them to the correct spot, then do the same for A/A and connect to the other?

Also, the 8908 is not well labeled. Obviously I will kill the power before doing anything, but is there a danger with having them on the wrong connection? Thanks!!
 
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Old 12-10-15, 06:48 PM
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I think I just realized something with the drawing -- do the colors in the picture you posted correspond to the color wires? Would you have the red going to and from the humidistat, then the two black wires (24 AC and A/A) connecting themselves? Thanks!
 
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Old 12-10-15, 07:04 PM
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Yes.... my diagram was to illustrate a connection method.

Red or black doesn't make a difference since we're dealing with an AC circuit here.
There is no polarity on the h'stat either.
 
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Old 12-10-15, 07:46 PM
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Thank you! I got it up and running without a problem, water is now flowing perfectly. Now my next question:

I see the water is flowing and it will shut off when I set it to off, but will flow pretty steadily no matter the set point. Being that it is in the 50-60s this week, will this continue to pump humidity into the air when it isn't really needed, no matter the number it is set on?

I assume the higher the set point, the higher the humidity, or does it work the opposite? The instructions say to have the setup at 40 when temp is at least 20 degrees (F)...I would assume the set point would say what humidity level you want it (which would work the opposite, since you'd want a lower set point in the summer, higher in winter.

Either way, set point is set at 40 and water is still flowing -- I just want to make sure I understand how it is going to work. Thanks again for your help!!
 
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Old 12-10-15, 07:58 PM
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The 24vac from the furnace is supposed to only be live when the furnace is running. Then once the furnace is running and the humidity is low.... the h'stat closes and allows the humidifier to run.

If the humidifier is running without the furnace running.... that's a problem in wiring that needs to be corrected. You'll need to post the make and model of your furnace,(found near burner) or open the blower door and either shoot a picture of the control board or post the model number for the control board. The area we are interested in is where the thermostat wiring (and humidifier) wiring connect. http://www.doityourself.com/forum/el...-pictures.html
 
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Old 12-10-15, 08:18 PM
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I apologize -- I think I worded that incorrectly.

Water is only running when the furnace is running. When the furnace kicks on, water flows, so we are good there.

My question I guess comes with how the manual humidistat works, and what I should expect. I have the humidistat set at a set point of 50 now. Will the humidistat always click water to flow, even when the extra humidity is not needed? I expected, based on the instructions, that it would not (since it sounds like I need to set a higher set point when the temperature is higher).

To me, it sounds like the humidistat should control the flow of water (maybe it always clicks on) but the flow level should be different based on humidity). Is this how it works?

If I want less humidity, I assume I lower the set point? This is really where I am confused, since the instructions give the example to set it 40 when its above 20 (as compared to 15 when its negative 20). I hope I am making sense -- I really appreciate your help!
 
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Old 12-10-15, 09:15 PM
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No problem.

The setting you set the h'stat to is the relative humidity that the humidifier will try to maintain. The water flow is either on or off..... there is no variable water feed.

As the temperature drops.... the amount of humidity in the air drops. If you try to put to much moisture back into the air it will condense on the windows and it could condense in the walls depending on the age and leakage of the house.

An automatic h'stat lowers the humidity level as the outside temperature drops. With a manual one... you set it based on outside temperature.

You just want to add enough humidity back to the air to keep the static electricity in check and keep it comfortable for breathing. Once it gets cold I fine tune mine almost everyday. I can pretty much tell from the feel of the air. I don't usually recommend setting it over 35%.
 
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