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How to wire duct fan to Carrier 58MVC100-20 furnace?

BeachbumBeachbum Member Posts: 3
Hello.  I hope someone can help me.

I want to wire a Suncourt 6" in-line duct fan into my duct to help boost airflow to an upstairs bedroom.  I want to hardwire it to the blower motor so it only comes on when the blower is on.  I have a Carrier Infinity 58MVC100-20 furnace.  It has a "variable speed" blower.  

I simply want to splice into the correct two wires at the blower motor harness(es) to connect the standard house wire that I ran from the Suncourt fan to the blower.  So very simply I need to connect the black wire to something and the white wire to something, and of course ground it.    

There are 2 wiring harnesses that plug into the blower motor.  One is a 4 pin, and the other is a 5 pin.  They are described below:

The 4 pin harness is marked +V (red wire), Tx (yellow wire), Rx (blue wire) and C (green wire).

The 5 pin harness is marked L (black wire), N (white wire), Ground (green and yellow wire), and the last two pins are jumped with a short piece of yellow wire.

Again, I want the in-line duct fan to ONLY COME ON WHEN THE BLOWER IS RUNNING, both for heating and cooling. 

Can someone tell me which two wires I need to splice into?

Thank you! 


  • HDEHDE Member Posts: 220
    Not that way

    Since you have a infinity furnace with a variable speed motor you can not wire to the motor leads easily because its a DCV variable speed.

    Look on the circuit board for a neutral connection (N) and one marked EAC ( electronic air cleaner) this will give you 120 volts switched on whenever the fan is running in heat or cool. Attach with 2 spade clips
  • BeachbumBeachbum Member Posts: 3
    Almost there...

    Thanks HDE.  I looked at the circuit board and see an empty male terminal marked "EAC-1" that is next to 2 other black wires connected to the board.  So I assume that is where my black wire should go.

    And there is an empty male terminal marked "EAC-2" in the Neutral2 block (outlined with a white line) on the board, next to 5 other white wires plugged into the Neutral2 block.  So I guess this is where my white wire goes.

    And I assume I can ground my ground wire to any nearby screw on the furnace chassis.

    Is this all correct?  Just want to make sure I don't fry something!

    Thanks again...
  • VictoriaEnergyVictoriaEnergy Member Posts: 126
    add ad relay...

    Check the amperage rating of the fan, if it's near or above 1 amp, then the EAC1 & 2 should power a relay 120VAC coil and then run a separate L1 through the relay contact to the fan and then back to the L2.

    The contacts for EAC are for an Electronic Air Cleaner and are only rated 1A max.  Overload them and you get to buy a new furnace control board...
    Home Owners Please Note:

    You are receiving advice from some very skilled pros completely free of charge. One of the reasons I participate is to sharpen my own troubleshooting skills. So; did we get it right? I would be grateful if you extend this courtesy back by posting the final outcome of the issue you are inquiring about. Thanks
  • HDEHDE Member Posts: 220
    Duct booster

    Your using an axial inline duct boost fan from suncourt right?

    Well below an amp

    Black Lead - Connect to HOT (L1) or EAC-1 when provided.

    White Lead - Connect to Neutral (L2) or EAC-2 when provided.

    Green/Ground Lead - Connect to Appliance Ground (Chassis)
  • BeachbumBeachbum Member Posts: 3
    All done...THANKS!

    Just finished wiring it up and my little Suncourt purrs like a kitten every time the blower comes on.  The duct fan only draws .35 amps, well under the 1 amp max., so that turned out to be a non-issue. 

    So I wired it exactly like you to EAC-1, white to EAC-2, and ground to the chassis.  My furnace even had a knock-out plug on the metal box that houses the circuit board, so I ran my 14-2 house wire through that and secured it with a cable connector for a nice, neat installation.  Added female terminals to the two wires and plugged 'em in...grounded the ground wire to a handy screw on the chassis...Done!

    Many, many thanks to both of you for your help.         
  • HKevinHKevin Member Posts: 4
    Quick question regarding this

    I have an Carrier infinity furnace as well and have the same control board. I can easily hook up the fans to the board but I have 2 fans each at .35amps. (still under the 1amp max)

    Is it safe to go ahead and tie in on the EAC1 and EAC2 being at .7amps or should I do a relay just in case? If I should do a relay can you point me to the right one? (I can wire it but not sure which to buy)

    Thanks in advance!
  • TechmanTechman Member Posts: 2,144
    Duct fan's

    I would be worried about "start up amps' w/ two duct motors. The EAC does not have "start up amps".
  • HDEHDE Member Posts: 220
    If Concerned

    Small residential duct booster fans with shaded pole motors don't draw much but you can use a RIB Relay

    120V coil/120v contacts SPDT or SPST or DPST or DPST- all will work

    The relay with the override switch is nice for turning fans off
  • John MillsJohn Mills Member Posts: 767

    We did this for an old guy on a Rheem, dang booster damaged to board. From now on, RELAY!
  • HKevinHKevin Member Posts: 4
    edited October 2013
    Ready, believe I know the answer but want to confirm..please help

    I have wired up one of my fans as was listed. (EAC-1 and EAC-2) I now want to wire the second fan and a relay (I finally got around to buying the relay) and want to confirm the wiring connections.

    I bought a 5 pin, 120V relay - White Rodgers 90-294Q. (see attached picture)

    I believe that what I want to do is:

    Pin # 1 - Connect the EAC-1

    Pin # 3 - Connect to EAC-2 AND neutral to fan

    Pin # 2 - Connect to Black Wire (Hot) Coming into Furnace

    Pin # 4 - Connect to Hot Wire out to Fan

    Is this right? Please let me know the right way to connect this to the furnace listed in this post.

    Thanks in advance,

  • HKevinHKevin Member Posts: 4

    Anyone able to confirm?

    Thanks in advance!
  • Paul SPaul S Member Posts: 1,229

    Yes you're correct ....1 & the relay coil connected to the EAC terminals from board.....and 2&4 is a normally open Dry contract you run 120 v through to power fan Paul S
    ASM Mechanical Company
    Located in Staten Island NY
    Servicing all 5 boroughs of NYC.
    [email protected]
  • HKevinHKevin Member Posts: 4
    Big thanks to Paul!


    Thank you for confirming the wiring. I thought I had it right but wanted to verify before running off and doing it.

    Things are running smooth and I have a warm room now :)
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