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Aprilaire 800 Steam Humidifier with Trane XC95M furnace and Comfortlink II TStat

Aprilaire 800 Steam Humidifier with Trane XC95M furnace and Comfortlink II TStat

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Old 11-25-18, 09:31 AM
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Aprilaire 800 Steam Humidifier with Trane XC95M furnace and Comfortlink II TStat

I have a Trane XC95M furnace with a 3-wire Comfortlink II communicating t-stat. I recently purchased an Aprilaire 800 steam humidifier which we had in our previous house and loved.

I installed that previous one myself but the old system used a standard t-stat not a communicating one. This time, I'm really stumped as to how I'm supposed to make the proper connections.

Converting to a non-communicating t-stat isn't an option as there are only five wires at the t-stat location (3 in-use and 2 not connected) and no means to get more there. (Not to mention losing some of the benefits of the variable speed fan control.)

The humidifier came with a return air duct-mount humidistat which I was planning to use as I can easily get the outdoor temperature sensor connected to it from the furnace room. Since the t-stat doesn't use the normal connections to the furnace, though, I'm confused as to how to get this to work.

Any suggestions would be appreciated.

Thanks.
 

Last edited by dukescotts; 11-25-18 at 11:14 AM.
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Old 11-25-18, 10:50 AM
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The important thing here is what model humidistat are you using ?
The 800 is a standalone humidifier.
If you want it to run when the furnace is heating it may require a relay.
 
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Old 11-25-18, 01:41 PM
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The Aprilaire model 62 humidistat came with the 800 humidifier and is what I was originally planning on using. It allows the humidifier to run independently of heating, kicking on the fan whenever it needs to call for humidity. (We live in Colorado, so that's a key part of this. In the daytime, with our intense sun, the heat rarely comes on, even on cold days.)

I'm open to using a different humidistat or even upgrading the t-stat if I need to. The instructions for the t-stat make it seem like it should be able to control humidity but there's nothing that describes how you'd wire for that.

Thanks.
 
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Old 11-25-18, 01:49 PM
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That humidistat will work ok. Can you take the cover off the EIM module at the furnace and post a picture of it for me. I need to see what it has for wiring used. How-to-insert-pictures
 
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Old 11-25-18, 02:43 PM
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Here are a few photos. Hopefully they show you what you need.

Thanks.
 
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Old 11-25-18, 03:37 PM
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Wow..... a budget job. Date/phone cable used for the outside condenser.

Thanks for the pictures. That's not just an EIM..... that is the processor board for the furnace. The service manual says when in communications mode...... the extra screws terminals cannot be used. This will not be a cut and dried installation. I'm not a Trane certified tech so I don't usually run across a request like this. I'm going to check into it further.

My forum partner, Houston, may have an idea. I left him a message.

Trane XC95 install manual (pdf)
 
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Old 11-25-18, 03:47 PM
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LOL. Yeah, the Cat5 cable for the condenser did make me laugh.

I've dug through that manual a bit and also figured out that the regular terminals are essentially non-usable when in communicating mode - thus the challenge.

I appreciate your help.
 
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Old 11-26-18, 08:31 PM
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Take a look at Fig 57 on page 45 in the manual that PJ posted.


Line 6 shows a 120VAC humidifier terminal and line 4 shows the neutral terminal for your 120VAC humidifier transformer.

If your humidifier doesn't have an external transformer you could use a relay with a 120 volt coil connected to these terminals to tie in the humidifier.

The next step would be to verify if these terminals can be controlled from the stat or are they always energized when a heating demand is present. ( the latter is more likely).
 
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Old 11-26-18, 08:35 PM
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Ok..... cool. Thanks Carlos.
Based on that information..... the humidistat can not call for the blower to run...... correct ?
Since he's using a steam unit..... he wants it to run more often than the heat itself.
 
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Old 11-26-18, 08:40 PM
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https://www.bayareaservice.com/wp-co...all-Manual.pdf

I see nothing to indicate humidity setpoint range on fig 2.3 of the thermostat manual.
 
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Old 11-26-18, 08:45 PM
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I guess Duke can keep the fan in the On position since this is heat mode.
 
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Old 11-26-18, 08:46 PM
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That may be the only way to way to accomplish this.
 
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Old 11-27-18, 09:03 AM
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Thanks Pete and Carlos. I had a quick minute to look in the furnace and did find what I'm pretty sure is the 120V humidifer connection. The wire heads up into the burner compartment and I'm assuming into the j-box in there but I didn't have time to do any more tracing or testing.

When I have a chance (probably tomorrow evening), I'll trace that wire and then get a meter on it to see what I get depending on what's going on with the t-stat settings. From the t-stat manual, though, it would seem that I should be able to set the desired humidity setpoint and get the fan to turn on when humidification is needed.

I'll also pick up a 120V relay to use.

I'll report back on what I find.

Thanks again.
 
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Old 11-29-18, 02:51 PM
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Got this all working! - thanks to the folks here and to a contact at Aprilaire.

For anyone who might run across this thread in the future, a few things to keep in mind:

1. You definitely need to use the humidity control from the Trane communicating t-stat. It is not possible (at least not in any reasonable way) to use an external, 3rd party humidistat.

2. The humidifier connection on the Trane furnace is a 120V connection. The Aprilaire 800 humidifier I used (and I'm sure many others) need a normally open 24V dry contact closure. If you were to connect 120V up directly to the humidifier, you'll fry it real quick. So, you need to use a relay with a 120V coil and a normally open "output." I used this one: https://www.amazon.com/Functional-De.../dp/B01L2MOI48

3. The wiring diagram in the furnace manual is incorrect. It shows a three position connector with "BK /HUM" at the top position of the connector and "BK / 5" at the bottom position of the connector. In reality, those are reversed. I started tracing the wire coming out of the "HUM" terminal and discovered that it went all the way up into the burner itself. Pulled the cover from the burner and figured out it went to the igniter. In the j-box inside the furnace, though, I found a wire that was actually labeled "HUM" right on the wire insulation. Traced that back to the terminal that was supposed to be "BK / 5". So, I pulled the whole connector and used the multi-meter on each one of the terminals with the t-stat calling for humidity and not calling for humidity. Sure enough, the bottom one ("BK /5") was the one that actually changed when the humidification call changed (120VAC when calling for humidity, 0VAC when not). This might be a board rev thing so I'd definitely recommend testing your terminals with a meter before making any connections.

Thanks again for all the help.
 
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