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  1. #1
    Join Date
    Jan 2019
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    1
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    Nest low voltage error

    Hi guys iam a new tech, i worked on a split system a carrier with burned contactor and bad dedrost board, replaced contactor and bypassed the board, got error message that nest is not getting volatage, i do have 28 v between red and common, the unit starts when i hardwire the thermostat wires (red+green+yellow)..i put an older battery powered thermostat the unit runs with it until i come back install the defroast board and try again with the nest.
    Any idea why the nest is not getting 24 v?
    Transformer is good, getting 240 and supplying 28v, hardwiring works,...

    Thanks!

  2. #2
    Join Date
    Jul 2019
    Location
    Oklahoma home its in the name
    Posts
    716
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    It's a hockey puck.

    Sent from mars using Tapatalk

  3. #3
    Join Date
    Dec 2007
    Posts
    9,300
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    Quite possible the NEST caused those issues.

    Trash the NEST and install almost anything but!!!!
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  4. #4
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    25,346
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    I saw the same thing on a heat pump. Low voltage to reversing valve caused it to vibrate and crack a tube. Dumped the charge, and the compressor ran until it cooked itself.

    That ended up being one very expensive Nest stat.

    Saw another one where the son gave his dad a Nest. Unit wouldn't work. Told the guy they were trash in commercial applications. But I could put a normal stat on if he wanted heat.
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  5. #5
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    25,622
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    NEST is POO
    Attached Images Attached Images  

  6. #6
    Join Date
    Nov 2019
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    1
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    Had one out here where the Nest would not communicate properly with the furnace (weak voltage). Ended up being a bad solder connection on the stat.

    Sent from my SM-G950U using Tapatalk

  7. #7
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    25,346
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    Oh yeah, just remembered another one. A co-worker was on this one split system, heat pump. Unit kept icing up outdoor coil. So I get sent out. Told customer I couldn't do anything for him until he changed out his Nest to a conventional, he wouldn't go for it, especially since there was a sister unit that was working fine.

    A week or so later the office calls me saying the unit was acting up again. Told them I did a write to change out the stat to conventional, was it approved? They said no. I told the office, then there was nothing I could do.

    Owner calls me and asks what's up. Told him. He said just go out there and change the stat. So I did. And left the Nest on site hidden on a top shelf. Unit began working fine. I think he ended up putting some other brand wifi stat on.

    That was probably over two years ago. Only been back to that roof once to get info on replacing another unit for the property management. Don't know what the guy ended up doing. Or if we even still have the account.
    If you were a real tech, you'd solder a relay on that board and call it good to go.

    I do a triple evac with nitro to remove non condensables.

    I use 56% silver on everything except steel.

    Did you really need the " If you were a real tech " ??

  8. #8
    Join Date
    May 2019
    Location
    Central, IL
    Posts
    34
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    We had a nest also low voltage on yellow , chattering contacter. Oddly it was intermittent problem.

    Nee pro 1 stat all good

  9. #9
    Join Date
    May 2018
    Location
    Elizabethtown, PA
    Posts
    96
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    I've seen Nests kill a couple of contactors and a fan relay. If there's a Nest and an electrical issue, the stat is where I would start.

  10. #10
    Join Date
    Jul 2018
    Posts
    14
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    I had a nest sending low voltage(<20vac) out on w. Changed tstat & had 28vac to furnace.

  11. #11
    Join Date
    Dec 2019
    Posts
    10
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    Quote Originally Posted by george3 View Post
    I had a nest sending low voltage(<20vac) out on w. Changed tstat & had 28vac to furnace.
    Also had one sending 16vac out on W, changed it back to the conventional thermostat to give them heat.

  12. #12
    Join Date
    Dec 2019
    Location
    westchester ny
    Posts
    33
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    go to settings and check your vin vout readings

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