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Thread: Nest 2nd Gen not working, introduce previously unused brown wire?

  1. #1
    Junior Member

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    Nest 2nd Gen not working, introduce previously unused brown wire?

    I'm trying to get a Nest 2nd gen thermostat to work with the HVAC in my apartment. The Nest is replacing a Totaline P474-1010 thermostat. My setup consists of a First Co. 30HX0-63 in the ceiling, and some sort of A/C unit on the roof of the apartment building.

    The wires that were connected to the old thermostat were as follows:
    Click image for larger version. 

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    Red -> R
    Green -> G
    Yellow -> Y1
    White -> B/O/W1
    Blue -> C

    Nest setup instructed me to wire things up as follows:
    Red -> RH
    Green -> G
    Yellow -> Y1
    White -> W1
    Blue -> C

    However, in this configuration I experience two issues:
    1. When the Nest is in Cooling mode, neutral/luke warm air is pumped out of the system.
    2. When the Nest is in Heating mode, there is no air pumped out, and no noise of any kind.

    I spoke with Nest on the phone, they recommended moving the white wire to the O/B slot.

    In this configuration, the system didn't pump out air in neither the cooling nor heating mode. Additionally, in heating mode there was a faint noise I'd describe as electrical.

    The Nest rep concluded that the First Co. system was incompatible with Nest.

    Disappointed, I began taking the wall panel apart to reinstall the original thermostat when I discovered further back in the wall was previously unused brown wire that came down with the rest of the wires.




    Is this anything I can use, or do I risk damaging my system by introducing this previously unused wire?

    Is it worth trying the red in RC or any other wire combinations, or does that also introduce risk for damage? (I rent)

    Thanks!
    Last edited by burnedpixel; 02-18-2013 at 02:43 PM.

  2. #2
    HVAC Thermostat Specialist

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    Quote Originally Posted by burnedpixel View Post
    Is this anything I can use, or do I risk damaging my system by introducing this previously unused wire?
    If your existing thermostat was working properly with out the unused wire connecting the unused wire will not correct the issues that you are having with the Nest.


    The Nest should be a compatible replacement thermostat for the Totaline P474-1010. Have you tried to reinstall your Totaline P474-1010 thermostat again to see if HVAC system still functions correctly?

  3. #3
    Junior Member

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    Quote Originally Posted by HVAC View Post
    Have you tried to reinstall your Totaline P474-1010 thermostat again to see if HVAC system still functions correctly?
    Just reinstalled the Totaline, everything is functioning normally as it did previous to the Nest installation.

  4. #4
    HVAC Thermostat Specialist

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    The firstco air handler may require a fan call with the heat energized. Still doesn't explain the AC not coming on in cool mode though...

  5. #5
    HVAC Thermostat Specialist

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    Sound like your Nest is defective. If we can determine that your system is a heat pump you could try to do a reset on the Nest. We have seen that a reset has fix some issues where the Nest is not able to detect wires. On the Totaline P474-1010 in the advanced setup what is 4 set to (on or off)?. If 4 is set to on this will tell us that your HVAC system is a heat pump.

  6. #6
    Junior Member

    User Info Menu

    Quote Originally Posted by HVAC View Post
    Sound like your Nest is defective. If we can determine that your system is a heat pump you could try to do a reset on the Nest. We have seen that a reset has fix some issues where the Nest is not able to detect wires. On the Totaline P474-1010 in the advanced setup what is 4 set to (on or off)?. If 4 is set to on this will tell us that your HVAC system is a heat pump.
    Excluding the clock, these are the settings I found in the advanced menu (as seen in this pdf, pg 10). I realize some of these may be inconsequential, but figured it'd cut down on the back and forth if I gave them to you in one post:

    Step:
    2 — 2
    3 — Off
    4 — On
    5 — O
    7 — 2
    8 — 2
    9 — d1
    10 — On
    11 — F

    Thanks again for your help!
    Last edited by burnedpixel; 02-18-2013 at 04:53 PM.

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