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    furnace problem (3 Posts)

  • steamfitter steamfitter @ 12:32 PM
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    furnace problem

    I have a Nordyne furnace and the service tech recently replaced a limit switch set at 225 degrees ( the old one was set at 205 degrees). I have a variable speed fan motor on a 72,00 btu furnace and the cfm setting was on 1050. The tech said he had raised that to the next level (which I believe was 1200 cfm). After several weeks I found the house to be quite dry and uncomfortable. I tinkered with the switches below and attempted to return it back to its original setting but I mistakenly set it higher (1500 cfm).

    After more discomfort I went down and realized what I had done and reset it at the original 1050 cfm. I also changed the air filter which was understandably pretty dirty.

    Now I'm not sure if it's just me or something is not right. Everything seems to be working but the fan speed sounds noisier and the dry and discomfort remains. Is it possible that something needs to be reset? I have turned the burner switch on and off, as well as the thermostat. With the weather changing so much ( dramatic rise and fall of outdoor temps recently) it's hard to judge if the forced air heat is working as it was in the past.
    I'm trying to avoid another charge/call to the furnace contractor.
    Thanks for any suggestions!
  • Spence Spence @ 1:25 PM
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    Furnace Issues

    The first thing that is not right is the limit. Unless approved by the manufacturer, NEVER raise the cut-out temperature.

    Dryness and comfort are independent issues. Check the thermostat reading against a high quality thermometer; the two should be within 3 degrees. Also check your TR and compare to the nameplate. The CFM numbers sound like the cooling dips, not the heating.

    Check your RH with a psychrometer; 30% is the lowest on the comfort scale. If you don't have one, cut the tip off a clean white shoe lace, soak it in water, and slip it over the wand of your thermometer for a wet bulb value. You'll have to convert to RH. For example, 63 degrees WB is 50% RH.
  • steamfitter steamfitter @ 12:10 PM
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    what is TR?

    Thanks for your help! What is TR? Is that temp. range?
    What is the negative effect of raising the high limit, as the tech did from 205 to 225 degrees? Can the furnace be damaged? I am considering calling the company to have the limit replaced with a new limit that is 205 degrees. Do you think it can shorten the lifespan of the furnace?
    Thanks again!
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