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  1. #1
    Join Date
    Feb 2005
    Posts
    1
    hello all

    the thermostat that came in my home was ancient, so i replaced it with a common Honeywell digital stat from the local hardware store. ever since then, the fan kicks on and off twice quickly after the heat shuts off under normal circumstances. this only happens in heat mode. i tried a different thermostat claimed to work with 99% of systems and got no change.

    i have four wires. one of them is blue, which i hook up to the yellow stat socket 'cos that seems like the obvious choice. i'm wondering if this logic is the problem.

    any advice?

    thanks in advance

  2. #2
    Join Date
    Mar 2004
    Location
    Grottoes VA
    Posts
    5,856
    This is not a diy site.


    -- please read the site rules.
    Karst means cave. So, I search for caves.

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,289
    The thermostat is likely not the cause of the problem. If you have an older natural draft gas furnace, the fan limit may be cycling from residual heat off the heat exchanger after the thermostat satisfies and shuts the gas off.

    Either that or the thermostat is controlling the fan rather than the furnace and is shutting the fan off when the gas valve closes. This will definitely cause the furnace to cycle on limit.

    You need a pro to check the furnace to check its operation.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,721
    Check your air filter.
    Contractor locator map

    How-to-apply-for-Professional

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

  5. #5
    Join Date
    Feb 2005
    Posts
    38
    I have installed 1 honeywell t stat that turned fan on as sone as it called for heat as far as the blue wire on y if it was on y before then yes other wise you have to check where it goes y is for a/c condencer

  6. #6
    Join Date
    Nov 2000
    Location
    Coastal Georgia
    Posts
    34,902
    Get the guy at the hardware store to come over.

  7. #7
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,289
    Oh man, I didn't see this earlier...

    i have four wires. one of them is blue, which i hook up to the yellow stat socket 'cos that seems like the obvious choice. i'm wondering if this logic is the problem.
    <shaking head>

    any advice?
    Yes. Put down the screwdriver and back away from the thermostat.

    Slowly.

    <reminds self to read post more thoroughly next time before replying>

    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  8. #8

    Hmm,

    If a guy tells me that he put the blue wire on th Y terminal I would think that there was no yellow wire in the cable and if he said that that was the obvious thing to do I wouldn't think that he was a moron because he knew when he took the wire off the old one that the blue one was used and that the Y terminal was used I would have to say that he probably has it wired right and is stuck on the problem that his furnace short cycles now, the most obvious reason for this is that the temperature at the stat is changing that quickly If thats the case you will need to either move the air flow or the stat.

    You may not have noticed it on the mechanical stat because the anticipator was set at a high setting to compensate for the problem. If you go into your manual for the stat they have an anticipator like function that allows you to set the maximum amount of cycles per hour your furnace can run. Although none of this means anything if you were trying to fix a problem with your furnace by changing the stat.

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