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Thread: 2nd Gen Nest running AC compressor when trying to heat

  1. #7
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    Thanks for the advice. So I got a little adventurous and took the back plate apart. There are a decent amount of electronics in that plate, so now I'm beginning to lean towards faulty plate. A co-worker had a similar problem as me with a first gen Nest constantly running his compressor.

    Update amazon now offers a free smart home consultation



    What I find interesting (probably due to lack of understanding how things operate) is, when the Nest tech had me swap Y and W wires on the plate, the furnace did not come on. If the Y terminal on the plate was stuck 'on', I would have thought swapping those wires would have cycled the furnace on, but it didn't seem to do that.

  2. #8
    HVAC Thermostat Specialist

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    The reason why the ac may have been coming on was that it may have been set to try to pull power though the circuit to charge the battery for the nest. When pulling power through the ac circuit it may inadvertently pulled in the contactor. It would likely not do have a problem through the furnace circuit if it were to try to pull power from there. I still recommend a new plate or whole different stat.

  3. #9
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    Just my .02 what what it is worth.

    I bought a first gen Nest in March 2012 and had no issues with installation or its use. 7 months later my Nest developed the same "a/c compressor" cycling when calling for heat as the OP. Called Nest and did over 3 hours tech support over 2 days and had a second new Nest sent out to replace my defective unit. Installed 2nd Nest and it again worked fine for 3 weeks and it again developed the same condition. Installing my original Carrier thermostat restored normal service so the Nest base plate has an obvious short in it. Eventually, Nest support resorted to claiming my Carrier forced air/gas heat 58MVP HVAC unit as being "not compatible" and stated the "newer" Nest thermostat model may be "more tolerant in voltage fluctuations." However, hearing that the OP is having the same problem with the "newer" Nest is disheartening to hear since I really want to get it to work again. I may have to wait for the "3rd revision" comes out.

    Just wanted to put this out there in case others are having the same issue or are considering buying a Nest.

  4. #10
    HVAC Thermostat Specialist

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    Stang, thanks for the reply with your story! This just furthers my thought that NEST and their support team not only have a bad product, but also have bad support.

  5. #11
    HVAC Thermostat Specialist

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    If they would just get rid of the "power stealing" option and require a C connection a lot of these issues would be solved.. But if they did that it would cost them sales to DIYer's since most don't want to open the air handler and hook up the C wire.

    Nest Learning Thermostat, 3rd Generation, Works with Amazon Alexa

  6. #12
    HVAC Thermostat Specialist

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    Quote Originally Posted by Servicetech View Post
    If they would just get rid of the "power stealing" option and require a C connection a lot of these issues would be solved.. But if they did that it would cost them sales to DIYer's since most don't want to open the air handler and hook up the C wire.

    completely agree

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