My old 1950 Rheem furnace was replaced this summer with a 2017 American Standard/Trane/Ingersoll Rand S9X2 95% efficient furnace.

I figured I would simply attach my 120v 8" booster in-line vent fan exactly as I did to the old Rheem.

No way! The power lines to the blower are inside the furnace, not readily available as on the Rheem. All the is is a "computer panel" with connections seen in the attached JPG drawing for one of the manuals.

I have the installation manual and the service manual, but neither provides a clue to how to connect a booster fan. I don't see a direct way to connect the booster to the blower.

I've tested the EAC and HUM connections for AC and DC current when the blower is running, but two voltmeters both read ZERO.

Anyone have any ideas? There's got to be some way to skin this cat!
I hope the attachment is readable.

 

May I ask why you need a booster fan? Often times they can be a band aid for a poor duct system.
And that can be fixed so no accessory fans are needed.

 

Welcome to the forums.

Roughneck raised a good point.

To answer your request directly..... I labeled your picture.

 

The booster fan may draw too much current for the eac terminals.

check the rating and see if there's a maximum load for the eac terminals.

you'll need a separate power source for the fan and an isolating relay if the fan draw too much.

a booster fan btw is a patch for lousy ductwork which often't doesn't work well.

 

The booster fan has been working very well for over 25 years. That's when I installed it. It was not installed because of faulty or dirty duct work. It was installed because the kitchen is about a football field away from the furnace -- and it is MUCH cheaper than buying a second furnace just for the kitchen. Without it, the kitchen basically gets no hot air. With it, it gets enough. I've even insulated the duct work to the kitchen just to help a little.

So please let's no go off on tangents. It works -- except I have a new furnace that needs a new way to connect it. It should be pretty simple since it is already installed, but apparently not as easy as I had hoped.

 

"The booster fan may draw too much current for the eac terminals.

check the rating and see if there's a maximum load for the eac terminals.

you'll need a separate power source for the fan and an isolating relay if the fan draw too much.

a booster fan btw is a patch for lousy ductwork which often't doesn't work well. "

I checked this out, and you are correct. The service manual says that the load on the EAC or the HUM cannot exceed 120v @ 1 AMP. I doubt that my 25 year old fan exceeds that, but I don't know.

Also, the LINE CONNECTORS and the NEUTRAL CONNECTORS already have plugs on them, so I don't see an immediate way to use any of them. Plus, they are all connected to different things according to the electrical schematic:

LINE CONNECTORS:
1 - TNS-H
2 - CIRC-H
3 - LINE-H

NEUTRAL CONNECTORS:
1 - LINE-N
2 - BLOCKED
3 - CIRC-N
4 - TNS-H

I have no idea what these abbreviations mean, and the manual offers no explanation. I will attach a copy of the electrical schematic:shortly.

I realize that I likely will need a 24v relay and a separate 120v power supply for the fan, but that is not a problem. Knowing where (and how) to connect everything is the issue. I really don't want to "burn out" the computer board.

 

 

The HUM and EAC terminals are a normally open relay contact.
They can be used for 24vAC or 120vAC with a maximum load of 1A.

There are many ways to accomplish what you want. I relabeled your diagram to show using a 24vAC relay. Of all the choices available.... this is the safest for the furnace control board.

You get the 24v from R and B. The 24v is switched thru the EAC contact.

 

Here is a more complete view of the S9X2 wiring. The first diagram (above) displays the "computer panel" which appears in the lower center of this diagram. The 120v AC input is center right. The blower is upper right.

The S9X2 has a transformer built-in to convert the 120v to 24v, but it uses both. The thick lines are 120v, while the thin lines are 24v.

The LINE CONNECTION and the NEUTRAL CONNECTION plugs are already used, so to use those, I would need an adapter of some sort. I fail to see why the NEUTRAL CONNECTION is labeled as "neutral" since power/current runs through it.

I hope this diagram shows up OK.

 

Huh ?

Yes..... power runs thru neutral in any 120v application.
I changed the original picture to reflect a 24v connection. Is that not what you wanted ?

 

It's just been a long day. I was confusing GROUND with NEUTRAL.

 

Here are two shots of my current "IFC" AKA "Computer Panel". The first is of the top where the 120v power comes in and also goes to the 24v transformer and blower (marked LINE), and the power goes out (marked NEUTRAL). It also shows the EAC and HUM connections (unused).

The second shows the bottom of the IFC where my simple, timed/programmed thermostat is connected.

I have a 24v relay on order from Pennsylvania -- I figured I would need one. So it seems pretty straightforward. I run a separate 120v line in and out of the relay -- like any household switch; and run the 24v wires from the furnace to the other set of poles on the relay -- like any household switch. Excuse my ignorance -- I've used a lot of household switches, but not relays.

I assume which wire is HOT and which is NEUTRAL makes no difference to the relay?????

You said I get the 24v from the R and B. The R is on the thermostat board. What is the B? Your diagram shows it using the R and O.

Thanks a ton.

 

I corrected my diagram. It was unclear on the first picture.
You want to use B/C for your common 24v connection.
So that would be R and B/C for always live 24v power.

You connect switched 24vAC from the board to the relay COIL.
You will use the contacts on the relay to switch the HOT power.
Neutral is not switched.

Since you are attaching a 24v isolation relay..... you will no longer get the 120v from the control board.

 

Thanks very much.

The only thing I worry about -- a little -- is the furnace's computer chip someday "dying". The computer in my car did it a while ago -- and all of a sudden the car was dead -- useless -- and there was nothing I could do about it, and no way to figure out what the problem was. I now carry a spare!

I hope you have a nice long weekend.

 

I would not use a 24v relay.

Only the EAC terminals are energized consistently when the blower comes on at the right time.

Hum = only active in heating mode.

heating control circuit, same thing and fan operation is delayed - booster would come on early and shut off with burners.

I would use a relay with a 120v coil.

Pjay max's diagram doesn't make sense to be, having it wired between R and C (powered on all the time) and having one side go to the EAC terminals which are 120v.

 

There's a certain amount of available pressure a fan can work against and the ducts should be sized based on length, airflow and available pressure.

When the duct system is properly engineered and balanced, booster fans are never necessary.

If a run is very long, the solution is to use a large duct and transition down just before the end to get the correct velocity.

I'm not suggesting you spend a lot of money to re-do ductwork but the booster fan is a patch whether it was put in 25 years ago or not.

if you're happy with the patch, continue using it.

----------------
BTW your contractor completely shortchanged you by not wiring the stat so you can run the fan without heat and using the board's timer instead of the thermostat to stage. (W2 and G not connected)

 

Well, I only spent about $30 for the fan, but larger ducts were not an option -- just not enough space. I consider myself lucky to be able to fit everything in the space I had. I suppose I could have considered ripping out numerous walls and ceilings, but I've done enough of that in my life, and I never gave it a thought.

The setup works fine, and all I want to do is connect the trusty old fan to my new furnace -- and leave my walls and ceilings as they are. I was hoping to simply reconnect a few wires -- with or without a relay. I can't possibly be the only person who has this type of situation, but getting straightforward answers seems more difficult than I would have imagined.

I hope you are incorrect about the approach listed above by PJmax, but I suppose I'll hear from others.

 

I'm really unclear on how he wants you to hook it up. "dry contacts" put there but usually the board supplies direct 120v power to those terminals.

I haven't reviewed the manual for your furnace and he may know things about it i don/t.

I may just be confusing you at this point.



The method i would use if the eac terminals are not dry contacts: a 120v coil relay and hook it up to the EAC terminals.

The fan can get its power from the furnace's circuit and the hot is cut by the relay.

 

The EAC and HUM connections are "DRY" contacts and supply no power. They are simply OPEN circuits that CLOSE when the blower motor is operating. The MAX load they can handle is 120v @ 1 AMP, but the only available power on the furnace panel is 24v -- from the thermostat connectors.

So a 24v relay is perfect for my 120v booster fan needs (which should arrive as soon as mail delivery is restored here in Colorado).

I draw 24v power from the thermostat panel to the EAC contacts, and then to the 24v side of the relay -- red lines in the first drawing. The neutral returns to the thermostat panel. This 24v circuit is normally OPEN, but CLOSES when the blower motor starts -- and OPENS again when the blower shuts off. The 120v booster fan is connected to the 120v side of the relay and is powered outside of the furnace.

The only question is where the 24v neutral return should be on the thermostat panel. PJmax suggests B/C, which I assume is correct. Can anyone confirm this?

 

B/C is correct.

...................................

 

One, hopefully final, question. I have received my relay, but of course it comes with no instructions -- merely an electrical diagram on the side. Having never used a relay before, I am at a loss as to which pair of contacts I attach to the 24v furnace side, and which to the 120v booster fan side. I have included two photos to show my dilemma.

I assume that the 1 & 3 contacts with the circular wire icon are used on the 120v booster fan side, and that the 2 & 4 contacts are for the 24v furnace side.

Are my assumptions correct? Or will I blow up the house?

 

Contacts 1 and 3 are connected to the coil. That is the 24v in.
Contacts 2 and 4 are the normally open switch contacts for the 120v.

 

As usual, I had it COMPLETELY bassackward.

Thanks again.

 

SUCCESS!!!

I finally received all the various parts I needed, and had the time to actually put it all together -- and everything is working perfectly.

I had lots of the parts I needed -- wiring, junction boxes, solder, etc. so I only spent about five bucks. The bigger issue was finding the time, and making sure that everything was connected correctly -- and thanks to all of you, I was able to do it -- just in time for the Winter Solstice.

It was a big relief to hear the relay click ON and have the booster fan turn on!

 

Good job. Thanks for letting us know how you made out.