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Fan/limit rising with fire off

Dbs Member Posts: 2
I have a 23 year old forced air unit. It short cycles at times. It also seems to do something quite strange. After the fan has cooled the heat exchanger and the fan shuts off the fan/limit dial will raise in temperture to 110 or 120 or more with the burner off. I have changed out the fan/limit with no change . How can the heat exchanger rise in temperture after it has cooled to 100 with no heat going to it? Thanks


  • tangled in wires
    tangled in wires Member Posts: 23
    edited December 2013

  • billtwocase
    billtwocase Member Posts: 2,385
    it can

    residual heat can hide. The blower should only cycle once more. What are your other fan/limit settings?
  • Weezbo
    Weezbo Member Posts: 6,232
    edited December 2013
    the spring type

    have been thru hundreds of thousands of off on tentionings or flexings so something that

    i added to my list of things to do long long time ago when checking a Furnace was to push it in and turn it way round to the right clock wise and hold it thru its return just to exercise it out beyond where it normally turns off and on at.

    cleaning them is not all that difficult to do , either ,

    Harvey homeowner is in awe of the things he notices , so be careful if you do that with the power on because it ''makes" . and breaks ...

    it is similar to getting a no heat and going over and plugging in the appliance .. they are often speechless because they know that They did not un plug it ...vibration and harmonics have their own way of doing things ...

    build up over time of layers of dust etc do not tend to help matters either .. so maybe you give it a try or shut the power off and take it out and clean it .

    see how that works out.

    *~//: )

    sometimes , things like to do what they have been doing... so it cold be the minor technicality is still in its environment that may have caused the old one to bind.

    i mean it IS possible....

  • billtwocase
    billtwocase Member Posts: 2,385

    I wouldn't rotate the fan limit manually. First there are instructions on it that tell you not to, second, it will throw your the control off even more. Replace it if it is in question
  • Dbs
    Dbs Member Posts: 2
    Problem solved

    Your right. I think my lower limit was too high at 100. I lowered the lower limit to 80 and the dial no longer turns up when the fan shuts off. I have an old round Honeywell thermostat. I turned the adjuster lever all the way to the left to 1.2. This seemed to correct the frequent running of the furnace and seems to be running normally now. Thanks My upper fan limit is 150.
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