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Furnace control board help

cjohnson
cjohnson Member Posts: 8
Good afternoon. I woke up to a cold house today so I checked the furnace and it has a low pressure fault code on it. I cycled power and tried it and my inducer motor won't turn on which I'm guessing is causing my low pressure fault. I checked for 120V power coming from circuit board terminals to the inducer motor on start up and get zero volts. I ran 120V test power to the inducer motor to confirm motor is good and it runs perfectly. So would it be safe to say I need to order a new control board?? The furnace is a ICP 2 stage furnace and its about 9yrs old. Thanks and appreciate and help!!

Comments

  • Tim McElwain
    Tim McElwain Member Posts: 4,480
    What is the make pf the board? Picture would help.
  • cjohnson
    cjohnson Member Posts: 8
    Hi Tim I will take a pic for you. Give me couple mins. Thanks!!
  • cjohnson
    cjohnson Member Posts: 8
    Tim it says file upload fails so not sure why. Its a .jpeg file and 3MB pic so not sure why it won't upload. anyways its a HK42FZ0192406 or when I look it up on oem parts its listed as a 1172551
  • cjohnson
    cjohnson Member Posts: 8
    Furnace is a ICP, model # H8MPT100F14B1
  • JUGHNE
    JUGHNE Member Posts: 8,948
    Two stage gas usually have 2 speed inducer motor. Usually start on high for any gas call and drop to low speed for low fire.
    Have you test run that motor on both speeds.......white & red....then white and black......never red and black together.
    If you have this set up anyway.
    cjohnson
  • HVACNUT
    HVACNUT Member Posts: 4,195
    Sounds like the board or the wiring harness to the IDM.
    Dumb question. You have the door switch closed while testing, right? Does the wiring harness plug into the board seperately or is it part of a 9 pin connecter? Do you have 115v at the IDM terminals at the board with the door switch closed and a call for heat?
    A 2 stage furnace probably has 2 or more pressure switches. Most are N.O. but some are N.C. A switch might be stuck open or closed interrupting the circuit to the IDM. If that's the case, is it failure of the pressure switch or is it doing its job and something else is going on?
    cjohnson
  • cjohnson
    cjohnson Member Posts: 8
    Hi HVACNUT, appreciate the response. Yes with covers off the door switch is held closed while doing all my checks. Once I close door switch the furnace LED on board pulses for about 15-20 secs then afer that the 3 blink fault code comes up which on the cover shows a low pressure fault. I'm guessing that IDM should start right away when door switch closed and calling for heat. giving the pressure switches time to see the right pressure is there. Googled it best I could and other guys say 120v should be on the HI speed going to IDM right away?? Just want to confirm that before spending $250 on new board and not being the issue. Thanks pal
  • cjohnson
    cjohnson Member Posts: 8
    There are 2 pressure switches and both should be N.O. I jumpered them figuring I could pypass the pressure switches to fool it but then I get a different fault code saying the pressure switches are N.C. when they should be N.O haha. Again IDM does not turn on for those 15-20 secs when trying it that way
  • cjohnson
    cjohnson Member Posts: 8
    Sorry JUGHNE just saw your comment now. Yes I tried 120v on both speeds of the motor and runs both hi and low perfectly. When I try closing door switch with high speed test power the furnace goes through its steps but eventually does down on soft lockout after 4 attempts. I'm assuming that's cause it wont switch over to low speed when needed cause I have the test power on the HI speed???
  • GW
    GW Member Posts: 4,303
    Sounds like a board.

    What happens when you jump your r and w? You hearing clicks ?

    Then the fault code?

    You have two hot lines going to inducer?

    Fan runs when you jump both speeds?
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
    cjohnson
  • cjohnson
    cjohnson Member Posts: 8
    Hi GW sorry not at home right now but yes 2 hot lines to inducer, 1 for HI and other for Low speed. fan runs in high and low speeds when jumpered. There is clicking but can't remember at what time it clicks. Will check for that when I get home and get back to you. Thanks!