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  • Bryant Furnace

    Low Voltage fuse shorts out. Can this be problem with circuit board, or always a problem with thermostat wires?

  • #2
    Re: Bryant Furnace

    it is usually a problem with one of the wires shorted to ground- to ducts, to the cabinet, etc. disconnect all wires at the circuit board. make notes of what colors go to what terminal. install new fuse and turn on power. if fuse blows:

    - check for shorted limit wiring. if good:
    - replace circuit board

    if fuse does not blow:

    - replace t-stat wiring
    ~~

    ... it was plumbed by Ray Charles and his helper Stevie Wonder

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    • #3
      Re: Bryant Furnace

      I would check all wiring and switches for shorts to ground using your volt meter. I have seen limit switches ground out with no visible arc.

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      • #4
        Re: Bryant Furnace

        Originally posted by abqplumber View Post
        I would check all wiring and switches for shorts to ground using your volt meter. I have seen limit switches ground out with no visible arc.
        ^^what he said.^^ The overtemp and access panel safety switches should be fed from the low voltage transformer as well as the thermostat. I had a problem with my furnace intermittantly blowing the low voltage fuse when I first moved into my house. Turned out a furnace repair company replaced the overtemp switch in the main heat chamber, and put it in upside down and it would intermittantly short against the metal case. If yours isn't intermittant, you should be able to narrow it down fairly easily by checking with a DVOM for continuity to ground(testing from low voltage ckt. to ground should show OL).

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        • #5
          Re: Bryant Furnace

          Thanks for all responses. I shorted R & W together and furnace works fine. I think it is the red wire
          that goes to a/c (contactor I think). I disconnected this wire and reconnected the thermostat and everything is fine. Is it commonplace that contactors go bad? Thanks

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          • #6
            Re: Bryant Furnace

            the contactor should only be energized during AC or heatpump usage. this is done from the y and c terminals on the board.

            Do you have a heatpump?

            yes, it is common to have the wire and/or contactor short out.
            ~~

            ... it was plumbed by Ray Charles and his helper Stevie Wonder

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            • #7
              Re: Bryant Furnace

              Thank you. I would like to learn more about contactors. I checked the impedance of from the wire going to the contactor to gnd. It was about 1K Ohm. So evidently, it is not shorted. Is this typical? What is the life of a contactor and how do you know if it is going bad. I have heard that pitted contacts can cause damage to the compressor, because liquid could get into the high pressure side and liquid cannot be compressed.

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              • #8
                Re: Bryant Furnace

                the ohm reading from a contactor varies from manufacturer to manufacturer. i cannot tell you what is good or bad. the life of a contactor varies as well. depends up the number of cycles and the conditions it is expected to work in - load, environment, varmints, etc. it is bad when it: causes low voltage problems; causes high voltage problems. pitting of the contacts has nothing to do with liquid getting into the compressor. it has everything to do with the electrical flow and amps drawn by the compressor itself.
                ~~

                ... it was plumbed by Ray Charles and his helper Stevie Wonder

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                • #9
                  Re: Bryant Furnace

                  Thank you.

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