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  1. #1
    Join Date
    Jul 2007
    Posts
    65

    Carrier 2-speed control board

    I had a call last week where I found a Carrier 8000 furnance with error code 33 Limit circuit fault. The Carrier t-stat had no display. I checked for power on terminal strip on board and no 24v on any terminals. I assumed the board was faulty and I replaced today, just to end up with the same result. Should there not be power off my terminal strip to at least power t-stat? I have no power from r,g,c etc to ground, but the blower runs. I checked the fuse and it checks out.

  2. #2
    Join Date
    Apr 2012
    Posts
    44
    Does the transformer power run thru the limit circuit before it gets to terminal strip?? If limit circuit fault (code 33) then u must have an open switch somewhere. That's where I would start anyway.

  3. #3
    Join Date
    Jul 2007
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    65
    Transformer 24V goes straight to board, If even say a high limit was open would that break power to t-stat?

  4. #4
    Join Date
    Apr 2012
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    44
    I'm not familiar with that particular board, just asking if the power did in fact get interrupted by the limit?? Its not normally the case, but wasn't sure on that 2 stage board. Its clearly something exterior of the board, unless u got a bad new one. Are you getting the same error code with new board installed??

  5. #5
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    1,453
    Quote Originally Posted by iceage View Post
    I had a call last week where I found a Carrier 8000 furnance with error code 33 Limit circuit fault. The Carrier t-stat had no display. I checked for power on terminal strip on board and no 24v on any terminals. I assumed the board was faulty and I replaced today, just to end up with the same result. Should there not be power off my terminal strip to at least power t-stat? I have no power from r,g,c etc to ground, but the blower runs. I checked the fuse and it checks out.
    Was there 24v from the transformer?

    What is fault 33 stand for? Blowers normally will run all the time when a high temp limit has tripped.

  6. #6
    Join Date
    Apr 2012
    Posts
    44
    Says 33 is limit circuit fault. And blower runs. I think u have an open limit somewhere, like the code said. Did u check all the limits and rollouts for continuity. ?? I think u may have replaced a good board

  7. #7
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    1,453
    Quote Originally Posted by ottawaair View Post
    Says 33 is limit circuit fault. And blower runs. I think u have an open limit somewhere, like the code said. Did u check all the limits and rollouts for continuity. ?? I think u may have replaced a good board
    I think you are right.

  8. #8
    Join Date
    Jul 2007
    Posts
    65
    No I didnt check all the limits for contintuity, I suppose you guys may be right it is possible I replaced a board that was working. What I dont understand is that if the transformer sends 24v straight to the board and not through the safeties first why would I not have power at my terminal strip and power at t-stat. It seems odd that for example during normal operation a limit opens why would as a part of this safety circuit power is disabled on my terminal strip on board and take the t-stat out of play, or maybe for all I know this is normal?

  9. #9
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    1,453
    Are you saying that you have voltage at the T-stat, but not at the control board?

  10. #10
    Join Date
    Jul 2007
    Posts
    65
    No power at t-stat, power on control board, but no power at terminal strip that is on control board. By the way an error 33 is an limit circuit fault which indicates a limit or rollout open and if open switch does not remake within 3 minutes than code changes to errror 13(which i did see occur)

  11. #11
    Join Date
    Apr 2012
    Posts
    44
    Good u got it going. Odd stat pwr is run thru limits. State powered thru furnace, no battery backup. ??

  12. #12
    Join Date
    Jul 2007
    Posts
    65
    No battery back up, stat powered by common thans for the help

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