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Old 07-06-2020, 01:51 PM   #1
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Wiring for Aprilaire 700 to Carrier Infinity


Hello all,
I’m planning to install an Aprilaire 700 in my Carrier Infinity furnace. I read through the humidifier and furnace/thermostat literature and have some questions on how to wire them. I’ve attached a proposed wiring diagram and some supporting text and information below. Thanks in advance for any help, suggestions, or answers to the questions below.

Humidifier: Aprilaire 700
Furnace: Carrier Infinity Model 59MN7A080V171214
Thermostat: Carrier Infinity SYSTXCCITC01-B

The Aprilaire humidifier comes with a transformer. The transformer input is 110VAC and the output is 24VAC. I’ll call one of the transformer output terminals HX-24 (for humidifier transformer 24VAC) and the other HX-COM (for humidifier transformer common). This transformer will supply the 24VAC to run the humidifier controller and water supply solenoid (There is a separate 110VAC plug that provides power to run the humidifier fan).

The humidifier control has several terminals that I will connect as follows:

1. R and C power terminals on the humidifier controller:
These are the power inputs to the controller. The humidifier instructions say to connect R to the furnace R terminal and C to the furnace C terminal. The furnace has a HUM and COM terminal so I would normally connect R to HUM and C to COM. HOWEVER, the Carrier thermostat manual says that a “24VAC N.O. Isolation Relay (DPST) MUST be used to prevent mixing the internal humidifier power with the indoor equipment transformer.” The instructions do not say where the isolation relay is to be used, but I am assuming it is between the furnace and the humidifier controller. So, instead of directly connecting R to HUM and C to COM, I’ll use the required isolation relay between the humidifier controller and the furnace terminals as follows:

The input or coil side of the relay has two terminals. These will get connected to the furnace HUM and COM terminals. The output or contact side of the relay also has two terminals. One will be connected to the humidifier transformer HX-24 terminal and the other relay terminal will connect to the R terminal on the humidifier controller. The C terminal on the humidifier controller will be connected to the humidifier HX-COM terminal.

What I expect is that when the furnace energizes the HUM & COM terminals, that will close the relay contact and 24VAC power will flow to the humidifier controller (through the relay instead of directly from the furnace terminals).

Using the isolation relay and connecting in this way will accomplish three things:
1) Power for the humidifier controller will be controlled by the furnace HUM and COM terminals.
2) The humidifier 24VAC power is not connected to the furnace 24VAC power and thus is isolated as required.
3) The humidifier will not draw too much current from the furnace and thereby possibly burn something out (The Aprilaire 700 specs say it uses 0.8 amps and the furnace HUM and COM terminals can only supply 0.5 amps maximum). The humidifier will draw up to 0.8 amp power from its own transformer and not the furnace HUM and COM terminals, which can only supply 0.5 amp.

QUESTION 1 – does the above (or on the wiring diagram) look like the right way to connect the isolation relay?

2. Two ODT terminals on the humidifier controller - These go to/from an outside thermometer. No confusion on these connections.

3. W terminal on the humidifier controller goes to the “W/W1” terminal on the furnace. No confusion on this connection.

4. G terminal on the humidifier controller. The humidifier instructions say to connect this to the THERMOSTAT G terminal.

5. The Gf terminal on the humidifier controller. The humidifier instructions say to connect this to the FURNACE G terminal.
QUESTION 2 on the above items 4 & 5: The humidifier installation wiring diagram does not have the furnace G terminal connected to the thermostat G terminal. However, the furnace/thermostat wiring diagrams I’ve seen show the thermostat G terminal connected to the furnace G terminal so I assume that is the way it is currently wired (I haven’t actually looked inside the furnace yet). If wired as shown on the furnace wiring diagrams, I don’t understand the distinction between connecting to one or the other – they are the same electrically. What am I missing? Or should I remove the existing wire between the furnace G terminal and the thermostat G terminal (assuming it is there) to make the installation conform to the humidifier wiring diagram?

6. The two H terminals on the humidifier controller. The humidifier instructions say to connect one H terminal to 24VAC power which I would get from the HX-24 terminal and the other H terminal is connected to the humidifier water inlet solenoid. The other water inlet solenoid wire is connected to 24VAC power, namely the HX-COM terminal. I assume that the result of the H connections to the transformer and solenoid is that when the controller internally connects/disconnects both H terminals, power flows/stops flowing to the water inlet solenoid and therefore water flows/stops flowing to the humidifier.

After the humidifier has been wired as above, I’ve read elsewhere that I need to go to the thermostat and use its menus to get to the “install mode” or “service mode” to let the thermostat know that a humidifier has been installed.

Question 3: Any errors or suggestions on the above wiring description or attached wiring diagram?

Question 4: Will the above wiring result in the Carrier thermostat controlling the humidifier (instead of the Aprilaire humidistat)?

Question 5: Will the humidifier come on not only when heat is called for but also when the thermostat just wants more humidity (i.e. the thermostat calls for more humidity and the furnace fan and humidifier turn on even though no heat is called for by the thermostat)?

Question 6: Is there a DIP switch on the furnace control board that needs to be set to let the furnace/thermostat know that a fan powered humidifier is being used (instead of a bypass humidifier)?
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File Type: pdf AFC Aprilaire Wiring Diagram(reduced).pdf (67.3 KB, 17 views)
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Old 07-06-2020, 11:25 PM   #2
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Re: Wiring for Aprilaire 700 to Carrier Infinity


I didn't read your entire post, but I skimmed thru it. Here are my thoughts....

Throw away the relay and the controller that came with the humidifier. All you need to do is hook the humidifier up to "hum" and "com" and figure out how to properly program your Infinity's thermostat to control it.

Easy peasy, and way better than what ever it was that you were trying to do.
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Old 07-07-2020, 08:32 AM   #3
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Re: Wiring for Aprilaire 700 to Carrier Infinity


Thanks for the suggestion but....
1. if I do away with the humidifier controller, will the thermostat alone be able to control the water inlet solenoid on the humidifier? Where do I connect the two wires from the humidifier water inlet solenoid? and
2. if I do away with the relay, the HUM & COM terminals can deliver 0.5 amps but the humidifier specs say it draws 0.8 amp so I think I'm asking for trouble with a direct connection of the humidifier to the furnace HUM and COM terminals.

I do like the simplicity of your suggestion though. My configuration got more complicated as I tried to follow the directions in the manufacturer's instructions.
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Old 07-07-2020, 09:13 AM   #4
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Re: Wiring for Aprilaire 700 to Carrier Infinity


isn't that a fan powered humidifier?

There's probably a separate power source and relay which turns on both the fan and solenoid.

you would have to check the install manual of the furnace and infinity control to see how to set it up.

Probably just the humidifier terminals and changing some settings on the infinity control.
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Old 07-07-2020, 09:50 AM   #5
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I'm kind of surprised to hear that the control board in the furnace isn't strong enough to open up the solenoid. I've got the non-fan powered version of that humidifier hooked up to my Infinity furnace and it seems to work fine without the extra relay. It's better to be safe than sorry though, so you probably should install the relay.

I wouldn't use the humidiatat that came with the humidifier though. You don't need it. Your Infinity controller will energize the "hum" terminal whenever it thinks you need more humidity.

Do you also have a communicating Infinity air conditioner, or is it just a standard A/C? If it is a communícating one it will also have an outdoor air sensor built into it, which it will use to automatically adjust the humidity settings so that your windows wont get wet when it's really cold out. If you just have a standard A/C there is a separate outdoor sensor you can buy to accomplish the same thing. Either way, I think using the Infinity controller is the way to go.
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Old 07-07-2020, 10:12 AM   #6
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Re: Wiring for Aprilaire 700 to Carrier Infinity


Yes, it is a fan powered humidifier and yes, it has a separate 110VAC line that gets plugged in to power the fan. I don't think the 110VAC powers the water solenoid as the solenoid has two wires that the instructions say to hook up to the humidifier controller. I think the solenoid wants 24VAC from the controller.
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Old 07-07-2020, 10:22 AM   #7
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Re: Wiring for Aprilaire 700 to Carrier Infinity


I don't know that the "control board in the furnace isn't strong enough to open up the solenoid" - I'm just going by the specs: furnace HUM/COM can supply 0.5 amp and humidifier can draw 0.8 amps. The humidifier specs does not say what draws 0.8 amps and if it is from 110VAC (which would be for the fan) or the controller/solenoid. So maybe I'm being overly cautious.

But even if the furnace HUM/COM can supply all the 24VAC amps that the humidifier/solenoid needs, if I connect the humidifier solenoid directly to HUM/COM wouldn't water always be flowing to the humidifier whenever there was a call for humidity? Wouldn't that flood the humidifier or is there a float or some other mechanism to stop the water flow when there is enough water in the humidifier tray?

The A/C is standard - non communicating.
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Old 07-07-2020, 11:26 AM   #8
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Re: Wiring for Aprilaire 700 to Carrier Infinity


The 0.8 amps is probably the main power to run the fan, the control board just provides signal to turn on and it'll be fine.



The board has a relay, the hum terminals aren't always energized.
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Old 07-07-2020, 05:37 PM   #9
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Re: Wiring for Aprilaire 700 to Carrier Infinity


The power requirement of that solenoid is only 2.3 watts @ 24 vac. That's 96 mA (.096 amps) so not worthy of a relay and separate power source.

The .8 amps is for the 120 vac line that supplies a small fan moter and a control board.
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Old 07-07-2020, 07:50 PM   #10
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Re: Wiring for Aprilaire 700 to Carrier Infinity


Quote:
Originally Posted by bfrabel View Post
Throw away the relay and the controller that came with the humidifier. All you need to do is hook the humidifier up to "hum" and "com" and figure out how to properly program your Infinity's thermostat to control it.
I agree, since you have an external transformer you can follow the wiring description for the bypass humidifier. Image below from your thermostat manual.


Wiring for Aprilaire 700 to Carrier Infinity-infinity.png
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Old 07-07-2020, 07:53 PM   #11
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Re: Wiring for Aprilaire 700 to Carrier Infinity


I should add that you don't need the transformer supplied with the humidifier.


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Old 07-07-2020, 11:40 PM   #12
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Re: Wiring for Aprilaire 700 to Carrier Infinity


You should have a spec. sheet that came with the humidifier showing circuit diagrams for various types of systems.

You won't use the HUM terminals on the furnace board if you have the digital control humidistat from Aprilaire, which you apparently do. It can start the furnace fan and control the water solenoid independantly. That feature can be turned on or off depending on how you need/want to operate the humidifier. Generally humidifiers work most efficiently if the furnace is in heat mode. Even so, this feature lets you run it regardless of what mode the furnace is in, if you think that is necessary.

You want to be sure to connect hot water to the solenoid valve for the best operation results.

You don't need to use the transformer they provided... your furnace transformer will be able to supply the power for this control system and solenoid, since it's a very small load.

You also don't need any isolation relay, that applies to different systems than yours.

I'll attach a marked up schematic of how you can wire your system by using the furnace transformer power that you will already have been required to bring to the humidistat control anyway. Since it's nearby, it's an easy jump over to to one leg of the H -H switch and in series with the solenoid. No point in having to mount and power up a remote transformer and add more wiring when it's not necessary.

That should go pretty smoothly for you. Post back if you need further.
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Old 07-09-2020, 09:53 AM   #13
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Re: Wiring for Aprilaire 700 to Carrier Infinity


Thanks for all the comments/suggestions. I've read them all and thought about this a bit more. I'm beginning to understand the first response from bfrabel that said to do away with the supplied humidifier control and transformer. And thanks to the explanation from surferdude2, it looks like the furnace HUM/COM has more than enough power (amps) to control the humidifier. This greatly simplifies things.

So, here is what I'm now thinking (and a couple more questions):
Wiring...
Install humidifier and simply connect HUM/COM directly to humidifier solenoid wires (I think that is what is shown in 57TinkerMan's diagram). Program Carrier Infinity thermostat to tell it a humidifier is installed.

Operation...
When thermostat calls for humidity, it energizes HUM/COM which in turn energizes humidifier and its solenoid. Energized humidifier solenoid opens to let water in and humidifier control board turns on humidifier fan. When thermostat determines humidity is satisfied, HUM/COM and therefore the humidifier is de-energized.

Question A: If it takes a while to satisfy the call for humidity (say 30-40 min), will water constantly be flowing through the humidifier to drain because the solenoid is energized that entire time? Or is there an internal mechanism within the humidifier (e.g. a float) that stops water flow into the humidifier if there is enough water in the humidifier evaporator tray?

Question B: I've looked at the thermostat wiring diagrams and it looks like there are terminals designed to use an outdoor temperature sensor. My Carrier A/C compressor does not have a temperature sensor built in. Should I just buy a temp. sensor and connect it to the Carrier thermostat OAT terminals? How necessary is the temperature sensor?

Question C: I'm still on the fence with regard to the isolation relay since the furnace instructions say one MUST be used. But surferdude2 doesn't seem to think one is necessary. The humidifier is plugged into 110VAC and that is an external power source that could somehow "mix" with the furnace power (through the solenoid?). I guess to be safe I should use one unless I can get further clarification on this point.

Thanks to all that posted for helping me think through the options and possibilities.
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Old 07-09-2020, 09:55 AM   #14
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Re: Wiring for Aprilaire 700 to Carrier Infinity


Surferdude2, thank you for the diagram, that makes it clear as to how to eliminate the transformer.

Can you clarify why you don't think the isolation relay is needed?
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Old 07-09-2020, 12:09 PM   #15
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Re: Wiring for Aprilaire 700 to Carrier Infinity


The diagram I gave was for installing the humidifier and using the digital control that came with it.

We need to cut to the chase here and zero in on how you want to go.

It's up to you decide whether you want the Aprilaire digital control or the Infinity system to operate the humidifier.

Up until now, you have been trying to combine the two controls and it's giving you plenty of confusion.

Since I have already shown you how to let the Aprilaire digitial humidistat control the humidifier, let's see how all that changes when you elect to have the Infinity system take over that control function.

Given that you can't have both, you can put aside the Alrilaire digital control and disregard all the thermostat wiring associated with it. You can also put aside the transformer that came with it. All of those functions will be taken over by the Infinity system.

To help you understand why all that equipment is not necessary, it is necessary to realize how the Aprilaire 700 (2008 models until present) works. Here's the key issue, the wires that are stubbed out for the solenoid connection are parallel wired to a relay on the AA 700's control board. That relay turns the AA 700's self contained fan on when the solenoid is energized from some remote 24 vac source. That make the AA 700 fully controllable by utilizing only those 2 wires stubbed out. That puts the control task to some other device, which in you case and with your choice, can be the Infinity furnace.

That means you only need to connect the stubbed out leads to the Hum and Common terminals of the Infinity furnace. That's the only new wiring you will need to connect. Use 18/2 jacketed thermostat wire for that. Polarity is not important since it's 24 vac.

From that point on, you will need to follow the instructions you have for the Infinity control system for setting up the humidifier.

The electrical burden of the AA 700 (2 VA) is well within the support level of the Infinity furnace HUM and Common output so no isolation relay and added transformer are needed.

Some people prefer to use the AA 700's digital control, especially if they are about to replace their furnace. Others like the ability to control the humidifier from the wall thermostat and rationalize that when the furnace gets replaced, the humidifier probably will too. Choose your own control based on your own situation. I like the Infinity control method since it makes for a quick and easy hookup. There are those who have trouble getting up to speed with the Infinity programming but I don't think you are one of those based on the intelligent way you have approached this isue.
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