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  1. #14
    Join Date
    Mar 2003
    Location
    North St Paul MN
    Posts
    858
    I think Carrier had a problem a few years ago with their stats. Wondering if the Bryant stat is the same. If I recall, it had to have a resistor across R and Y? Or W and Y? I can't remember...
    I'd rather have a bottle in front of me, than a frontal lobotomy.

  2. #15
    Join Date
    Apr 2003
    Location
    Iowa
    Posts
    763
    your stat has a jumper from RC and RH doesn't it?

  3. #16
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Is the thermostat that was on there a power stealer type with no common?
    If so, there was a resistor you were suposed to install between C and W at the control board. Without the resister, power stealer thermostats can be flakey in the cooling mode on systems with a control board in the AH/furnace since there may not be a good low impedance electrical path from the W terminal on the control board through the controls to common. Power stealer thermostats have to "fake" a common to work. On a control board the 24v from the thermostat usually goes to a transistor on the board to "switch" the power on to a relay coil on the board, so there isn't a good electrical path for the thermostat to fake a common through..
    The odd thing is, sometimes you can have 2 units with the same board, and it will work fine on one but not the other...

    You also need the resistor on AS/Trane air handlers because there is NO electrical path to common from W until the fan relay closes.

    There generally isn't a problem in the heating mode since it can fake a common through Y, wich is always low impedance to common through the contactor coil in the outdoor unit.

    If you have a way to actually measure the impedance between W and common, generally if the impedance is over 25z, you need the resister, if it is below, you don't need it.

    I don't think I have ever seen a meter that can measure impedance that would be in a HVAC techs collection, so I follow a simple rule for power stealer thermostats.
    If W goes to a control board, or the air handler requires a call to G in the heating mode, install the resistor


    It scares me that I remember this crap....need a life.
    If more government is the answer, then it's a really stupid question.

  4. #17
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,247
    Originally posted by mark beiser
    It scares me that I remember this crap....need a life.
    Sounds like commitment to your profession.
    Keep the post coming they are great.
    Have you set up a Google alert for Carbon Monoxide yet?
    Click here to find out how.

  5. #18
    Join Date
    Dec 2001
    Location
    Cartersville Ga
    Posts
    1,035
    bryant stat used common to power up, W/R uses batteries this must be the difference

    i will go out there tomorrow, will post results


    mike
    In the land of the blind the one eyed man is King! semper fi

  6. #19
    Join Date
    Mar 2003
    Location
    North St Paul MN
    Posts
    858
    Originally posted by mark beiser
    If so, there was a resistor you were suposed to install between C and W at the control board.
    Yea, that's what I was thinking. Seems to me it's a 1K resistor if memory serves me right.
    I'd rather have a bottle in front of me, than a frontal lobotomy.

  7. #20
    Join Date
    Dec 2001
    Location
    Cartersville Ga
    Posts
    1,035
    common was used on all these stats, so resistor was not used.

    had one again, now 3 times. in every case, using a w/r fixed it, but builder demands bryant on every stat, unit, even humidifier.

    never saw this before, now 3 in 10 days. all of the other units in the 4 subdivisions are working like they should. we are pretty high volume, in my opinion (43 roughs on 2 system townhouses last week), so i see a variety of problems, but this is killin' me!

    In the land of the blind the one eyed man is King! semper fi

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