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  1. #1
    Join Date
    Jan 2019
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    Trane XL90 has 2 pressure switches, only one with continuity. Is this unsafe?

    I have a Trane XL90 which was blowing cold air. The red light was flashing 3 times which apparently indicates a draft pressure error. First I noticed water on the bottom of the inside of the unit beneath the box where the drain hoses meet and which has a hose exiting the unit. I cleaned out the box as instructed in a guide elsewhere but it was still blowing cold. Then I made sure the hoses to the pressure switches were unobstructed and checked the continuity of each switch when I turned the furnace on. One has continuity and the other doesn't. The furnace is now working and I plan to have a professional come out as soon I can get someone on Monday but I want to know if it is safe to run it in the meantime with only one pressure switch operational.

  2. #2
    Join Date
    Aug 2002
    Location
    Southold, NY
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    Some switch’s are normally open some closed. If there was an issue with the switch it wouldn’t fire up.

  3. #3
    Join Date
    Nov 2006
    Location
    Athens, Ohio
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    It is safe.
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  4. #4
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    Jan 2019
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    Thread Starter
    What I should have said is that when the furnace kicked on the continuity numbers changed on one switch but not the other. They both started out reading 1 but one of them changed and the other did not. Does that make a difference?

  5. #5
    Join Date
    Jul 2007
    Location
    Virginia
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    Quote Originally Posted by jabraben View Post
    What I should have said is that when the furnace kicked on the continuity numbers changed on one switch but not the other. They both started out reading 1 but one of them changed and the other did not. Does that make a difference?
    If you are electrically troubleshooting the problem with this furnace, we cannot provide any assistance on what is, or is not, normal with these pressure switches when it is operating.

    This forums rules do not allow us to provide guidance with these type of DIY questions.

    The pressure switches are there to shut the furnace down if an unsafe problem arises, so in most cases, you are O.K. to let it operate until your tech comes out and looks over the unit.

    If at any time you are uncomfortable with letting it operate, shut it off until the tech arrives.
    Instead of learning the tricks of the trade, learn the trade.

  6. #6
    Join Date
    Jan 2019
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    Thread Starter
    Fair enough. Thanks for the information.

  7. #7
    Join Date
    Jan 2019
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    Thread Starter
    Tech came and confirmed that it was in good working order. Apparently my two-stage system kicks into the second stage after it has been running for some time, which my continuity test didn't take into account. He said the inducer speeds up at that point, thus acting on the second switch and kicking my burners up to their full capacity. Thanks everyone for the information.

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