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Discussion Starter · #1 ·
I broke the drain spud on my HEIL manual power humidifier, so I decided to replace the whole thing with a new Aprilaire 700M (which looks to be the exact same unit). However when the Lennox iComfort tstat calls for humidity, the new Aprilaire is unresponsive. No solenoid or fan movement. I'm a novice, but thought it should have been an easy swap since only 2 wires. I opened the blower panel on my Lennox SLP98V and didn't see a 24 VAC
Transformer installed for the HEIL, and noticed one was supplied in the Aprilaire box. Maybe that is required for the Aprilaire, but not the HEIL? From the control panel, there is a Totaline P283-0290 Fan Relay in between the panel and humidifier. Pic is included. Any ideas?
 

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You need a extra 24 volt transformer for the AprilAire.

You said one was installed for the Heil? Is it still connected? If it is then you can re-use it unless it is weak or faulty. I would put the new one AprilAire gave you in.

The relay is to isolate the transformer from the furnace as the earlier models of the SLP and Icomfort needed isolating.

Wire it this way:

Transformer from the Heil or the new one to 120 volt power to the furnace.

Then the (2) 24 volt wires from it go as follows:

1) to the isolating relay ( left side now ) and then from the other side of it to the humidifier and then from the humidifier back to the transformer

The IComfort should turn on the isolating relay and complete the circuit/
 

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Discussion Starter · #3 ·
Thanks for the feedback. The install with the HEIL did not need a transformer, so I will have to add one. After installing transformer to continuous power, I need to add it to the line of the left white wire connected to the relay? Essentially pull the white wire from the left terminal on the relay, connect it to one side of the transformer then from the other side of the transformer to the relay?
 

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It looks like to me that the relay coil is 24 volt and it is now being powered directly from the humidifier lugs on the furnace control board. If that be true, you can run the AprilAire off of those lugs without any relay or transformer needed. Perhaps the relay is doing something else that I'm not seeing but whatever it is, it must be low voltage since the switch leg running off the relay is stat wire.

Without seeing the whole wiring scheme, it's hard to be sure how it was wired to do whatever before with the Heil. I'm not familiar with Heil units so take this for what it's worth.

I do know something about AprilAire units. The 700M unit that you have has pretty good instructions for installing the unit and different schemes for controlling it. The control circuit of it usually runs directly from the humidifier terminals on the furnace board if they are 24 vac, which yours are. They leave you to your own imaginations as to how to supply the 120 VAC that the 700M also requires. A switched receptacle that comes live when the blower start is nice, do you have that now? If not the fan in that unit will run continuously. Check the installation instructions out and if you still have questions, post back.
 

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It looks like to me that the relay coil is 24 volt and it is now being powered directly from the humidifier lugs on the furnace control board. If that be true, you can run the AprilAire off of those lugs without any relay or transformer needed. Perhaps the relay is doing something else that I'm not seeing but whatever it is, it must be low voltage since the switch leg running off the relay is stat wire.

Without seeing the whole wiring scheme, it's hard to be sure how it was wired to do whatever before with the Heil. I'm not familiar with Heil units so take this for what it's worth.

I do know something about AprilAire units. The 700M unit that you have has pretty good instructions for installing the unit and different schemes for controlling it. The control circuit of it usually runs directly from the humidifier terminals on the furnace board if they are 24 vac, which yours are. They leave you to your own imaginations as to how to supply the 120 VAC that the 700M also requires. A switched receptacle that comes live when the blower start is nice, do you have that now? If not the fan in that unit will run continuously. Check the installation instructions out and if you still have questions, post back.
Some of the earlier SLP units you need a isolating relay as the furnace transformer is not strong enough or the relay in the board is not strong enough plus there was some issues with some of the IComfort thermostats.

I never ran into a problem but Lennox said the relay was needed.
 

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Thanks for the feedback. The install with the HEIL did not need a transformer, so I will have to add one. After installing transformer to continuous power, I need to add it to the line of the left white wire connected to the relay? Essentially pull the white wire from the left terminal on the relay, connect it to one side of the transformer then from the other side of the transformer to the relay?
It is a series circuit.

#1) you take one wire from the transformer and hook it to the relay on the left side. It may say R on the transformer and is Hot. If not don't worry as it is not polarity sensitive.

#2) you take a wire from the other contact on the relay and run it to the humidifier so it is now hot.

#3) you take the other wire from the humidifier and put it on the other side of the transformer which if it has a terminal labelled C you can use it. It is Common.
 

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Thanks for the insight yuri! I'm not real deep in specific furnace knowledge as you can tell. It's good that are here to fill that need. I spent most of my career doing commercial installations of refrigeration and electrical systems.

I'm still wondering if his old unit had a switched 120 outlet since the AA700 will need one unless he wants to have the fan running all the time. It's hard to run a switched line voltage feed out of a furnace without violating several code and safety rules! It has to be done via class 2 LV control wiring to a remote relay that is properly installed to code. Easy enough, might be a little challenging for the typical homeowner.

Evidently AprilAire didn't want to include a transformer and a relay in the 700 unit, which would make it a more complete system. Seems they just took the easy money and ran! :biggrin2:
 

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I am not familiar with these powered humidifiers as they are rare as hens teeth where I am.

Too expensive and not necessary as 99% of the time we use bypass units.

I imagine it has 120 volts to power the fan BUT it has a board/relay inside which is activated by the 24 volt signal from the humidistat. That will turn on the fan and open the solenoid.

I worked in a Convention center with a full blown Siemens DDC BAS system and VFD drives and all kinds of fancy equipment.

Variable speed drive VFD chillers and I also worked in a hospital with 600 volt 3 phase. We had electricians on staff but yeah resi is child's play compared to institutional and commercial units.

Now I am too damn old to be doing that stuff anymore.:vs_laugh:
 

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Discussion Starter · #9 ·
Additional photos for reference. You can see the HEIL is the same as the Aprilaire. Like they came from same OEM manufacturer. Which is why I'm surprised the Aprilaire needs the extra power. They both were plugged into the same constant hot standard outlet. The fan and solenoid would kick on only when the furnace started heating (blower is always set to ON or Circulate). However I would eventually like to wire it where the humidifier kicks on when I need humidity and the blower is set to ON, regardless if heating. I think it would be more effective that way.

Looking inside, I don't see any 24 VAC transformer. Not sure if Lennox has something built-in already.
 

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You have now run up against the problem that I thought you would. It seems that AprilAire doesn't want to get involved with whatever you decide to do or not do about controlling how their 700 model gets 120 vac power. I suspect they are concerned about the liability involved but that's just my opinion. As you have seen, the Heil unit LOOKS like the AprilAire one and may indeed be made by the same manufacturer but for some reason AprilAire decided to gut the unit of all 120 vac control... i.e., the relay and transformer.

Restoring the switching control of the 120 vac that powers the humidifier isn't all that hard if you have some basic electrical skills. It will require a relay and an enclosure box to mount it in. It will also require an extension ring on the outlet where the humidifier plugs in and the necessary fitting to get power to the new relay box. If you're up to doing that kind of work, it's no big deal. The relay can be a basic SPDT 15 amp 24 vac coil "ice cube" type that commonly sell for less than $10. Then an approved enclosure box w/lid is easy enough to get. The control voltage from the furnace control board humidifier prong and its associated neutral will have to be routed to the box. That's roughly one way how it could be done.

There is even a device sold that is called a "Relay In A Box" that could be used for this application but the ironic part is, you would still need to get a box installed in the same manner as before since the Relay In A Box doesn't actually include a box and it costs much more than an "Ice Cube" relay.

There are other ways to do this but most of them require you to derive line voltage from the furnace wiring. That can get you in trouble in some situations if not done in a specific way and will almost always void any warranty of the furnace. That would obviously be much easier, but I won't encourage you to do it that way.

If you choose to call or write AprilAire about this issue, I wouldn't blame you a bit! This product is being marketed with fewer components than necessary which ends up making it cost consumers much more to install than they will normally foresee.

SD2
 

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However I would eventually like to wire it where the humidifier kicks on when I need humidity and the blower is set to ON, regardless if heating. I think it would be more effective that way.
That can be done but you will really be building a kludge! Take my word for it, if you supply hot water to the humidifier, there will never be a need for you to run the unit any more than when the furnace is in heat mode.

SD2
 
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There are 2 versions of those powered units.

One uses a basic humidistat the M/maunal model and the deluxe Automatic/A model.

The A model uses a fancy outdoor temp compensated automatic deluxe humidistat on some versus the basic on/off one of the M/manual model.

The Heil may be the A automatic model which has a circuit board inside and may have it's own 24 volt power supply from the board.

Lennox uses Honeywell units and rebrands them and ICP/Heil probably is in biz with AprilAire.

On demand humidifying is not that feasible but there is on demand de-humidifying with using a outdoor AC in the summer. More for the really expensive systems and the SLP can do that with the proper IComfort thermostat. However you usually want a 2 stage AC if you are doing that or you will overcool your house.

Get the model # of the Heil and see if it is A or M.
 

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that modulating unit should be heating the majority of the time so you shouldn't need to run the humidifier without the heat.

With room temperature air evaporative humidifiers aren't very effective anyhow unless you feed them hot water which can get expensive.
 
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Mcgizzle, Can you post a picture of the hookup diagrams you find in the installation instructions that came with the 700M unit? There may well be different versions of that beast and you may be lucky enough to have one with all the stuff you need already set up and ready to go.

If you can open the unit up and check to see what gives inside it would be even more informative. A picture may help there also. All that I can find on the net only shows the cover removed with the fan & cord on it. If that has some method to plug it into the main body, then there is hope that there are some other components in there like maybe the transformer and relay we need hiding behind some cover that isn't shown in their literature.
 

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I finally found some instructions for installing that unit! Google finally came through!

It sounds like it's not going to all that bad after all. Here's the gist of it:

<snippet>
In order for the humidifier to turn on, the
furnace blower must be operating and the
control must be calling for humidity. The
interface between the Model 700 Humidifier
and the furnace to detect blower operation
can be accomplished several different ways:

A. If the humidifier is plugged into a continuously
powered 120 VAC outlet and the control is
powered from 24 VAC “ACC” or “HUM”
terminals on the furnace connected to the “R”
and “C” terminals on the control, then the brown
wires from the humidifier can be connected
directly to the “H” terminals on the control.

B. If the humidifier is plugged into a 120 VAC
outlet that is powered only when the furnace
is on, then the humidifier control can be
powered by a constant 24 VAC source
connected to the “R” and “C” terminals on
the control, and the brown wires from the
humidifier can be connected directly to the
“H” terminals on the control.

C. If the humidifier is plugged into a
continuously powered 120 VAC outlet and the
control is powered from a continuous 24 VAC
source, then a Model 50 Current Sensing
Relay (not included) must be installed in the
humidifier circuit. (Brown wires connected to
“H” terminals on control.)
</snippet>
 

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Discussion Starter · #16 ·
Interesting! While I try and figure out where to add the 24 VAC, I decided to put the old HEIL fan on the Aprilaire base. It fit/mounted perfectly and it fired right up! When the furnace started to heat, the HEIL fan kicked on and the solenoid on the Aprilaire base activated. Works just as it used to. So the HEIL fan assembly must have 24 VAC built-in.

I have this new Aprilaire plumbed to hot water, so I am OK leaving it wired where the humidifier only kicks on when furnace is heating. Just need to figure out where to add the 24 VAC transformer in line and if it can be continuously powered. The fan assembly is plugged into a continuous power 120 VAC outlet.
 

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I don't have the install manual for your unit in front of me but if there is a spot labeled EAC - electronic air cleaner then you can connect your transformer there.

It gets powered up when the fan starts'

If you have the manual then search it and they should show you where to connect to. There are 3-4 versions of that unit now and the wiring is not all the same.

You can connect it to the power coming into the furnace also.
 

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Discussion Starter · #18 ·
I worked up a CURRENT wiring scheme (without the use of the 24V Trans), then a PROPOSED wiring scheme with the Aprilaire supplied 24V Transformer. Do you think I can try the proposed setup? I also include a diagram of wiring supplied by Aprilaire for reference.

Let me know what you think. Thanks!
 

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Looks good to me (the one using the transformer). Their own diagram implies that power will need to be provided to the brown wires and you're doing that from a transformer via a relay switch that is controlled by the furnace board.

Since they aren't so kind as to show a schematic or pictorial diagram of the inside of the humidifier, it's hard to say for certain if they have a relay inside that controls the 120 vac fan or perhaps a sail switch. If not, it'll run continuously... I guess we'll know soon enough.

SD2
 
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