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IFC board problem

Trane TUH2D LP furnace IFC board indicates reverse polarity after 1 sec. into prepurge.  Checked grounds and neutrals for stray voltage, none indicated on Fluke meter.  Purchase new board, same results.  Trane said stray voltage over 2 volts.  Installing new board , did not connect ECM2 harness just in case .  Again after 1 sec prepure, 6 flashes and cycle stops, then repeats again .  How would the dual pressure switches affect in this way?  We installed this furnace 16 months ago, no problems last year.  Please suggest.


  • Tim McElwain
    Tim McElwain Member Posts: 4,621
    Reverse Polarity has nothing to do with

    stray voltage. It is the hot and ground being reversed. Go from the L1 (Hot) connection to ground you should read 120 volts, then neutral to ground should be zero. If it is the opposite then switch the wires.

    Any voltage on the neutral leg will cause problems with the microprocessor on the IFC board. Get an electrician to find out were the stray voltage is coming from.

    What is the make and model of the IFC board? Is this a two stage system?
  • Tim McElwain
    Tim McElwain Member Posts: 4,621
    Jack responded

    Thank you for the reply Tim. I cannot reply on post for some reason? The post is IFC problem. The polarity is correct. This is a 2 stage system. The board is WR50V64-507-90 also CNT-05160 . Trane thinks it could be the blower module is bad and to also ohm the 3 blower wires for near equal ohms. Feel free to post this , Tim as I can't . Thank you again . Jack.

    I called Jack and it seems that the hot surface igniter has been replaced and solved the problem. I am not so sure that is the solution so I am asking him to get exact numbers on the White rodgers Integrated control.

    Hopefully more to follow later.
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