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  1. #1
    Join Date
    Aug 2007
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    Number of wires needed for two stage stat

    Hi all,

    Had my Lennox G61MPV installed and an Aprilaire model 8366 2 stage stat. I heard one of the installers tell the other that I only had 4 wires coming from the stat to the furnace and the new furnace required 5 but he said he'll just jump one of the wires so it will work.

    I didn't question it then but I am now since it seems like the furance only runs in one speed, high. The manuals from both the furnace and stat show they need 5 wires and I actuall called Aprilaire who confirmed what I was reading.

    Can you please tell me what is the correct number of wires needed and if this jumper they put in actually allows the furnace and stat to work correctly.

    Thanks for your thoughts!

  2. #2
    Join Date
    May 2000
    Indianapolis, IN, USA
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    He's crippling the operation of the 2 stage furnace by using the timer.

    2 choices:

    they can use a "add a wire" device to double up 2 functions on 1 wire


    use a Vision Pro IAQ control which only needs 3 wires

  3. #3
    Join Date
    Jan 2004
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    What baldie said.
    Contractor locator map


    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    Jan 2007
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    That particular furnace has a jumper on the control board to time on the second stage heating cycle. The jumper I believe will delay it 10 to 15 minutes. Furnace will run in low fire (1st stage) for a selected amount of time then kick up to high fire (2nd stage) after the selected delay. Now, if they jumpered the w1 and w2 terminals then the furnace will only run high fire and never low fire. (which is defeating the purpose of the two stage furnace). You need a new stat wire ran. Preferably an 8 conductor wire to ensure plenty of wires for almost any type of system. You can run the furnace with the control board's jumper and be ok since the 10 or 15 minute delay will usually suffice in maintaining your room temperature before high fire engages. Have them remove jumper from w1 and w2 and use the control boards jumper or run a new stat wire and hook it up properly. The extra stat wire is for turning on high fire only when needed.
    Believe none of what you hear and half of what you see.

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