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  1. #1

    Carrier Infinity 98 - Low Fan Noise

    My recently installed Infinity 98 (59MN7 series) has what I think is a noise issue.

    I leave the fan on 24\7. LOW speed at night, and MED during the day. During the night (LOW) it makes a periodic noise (comes and goes). The noise is sort of a warble-resonating-whir noise. This happens when the heat is on or off and is not the inducer noise. I'm wondering if the fan needs balancing or other? Or can the LOW speed fan rpm be adjusted up slightly to hopefully eliminate the resonate noise?

    Please advise, thanks.

  2. #2
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    This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

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  3. #3
    Join Date
    Nov 2010
    Location
    N. Idaho
    Posts
    586
    Could it be your condensate pump that you're hearing?
    "I've got my Gas Mechanics license"
    "Yea, well my 16yr old daughter has her drivers license, doesn't mean she knows how to drive"

  4. #4
    It's not the condensate pump, the sound has a higher pitch than my pump.

  5. #5
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    Is the supply and return plenum lagged (insulated) It could be a very specific resonance/vibration when the blower hits a certain RPM.

    Depending on ductwork design, if your static pressure is on the high side, the blower might be surging/hunting a bit trying to maintain the correct CFM. With good ductwork, on low fire or low speed fan, the static pressure should be under 0.2"

  6. #6
    Not sure on the nomenclature, but I have the "rubber" between the horizontal runs and the vertical ducts running to and from the furnace.

    I'll discuss the static pressure idea with the service person next time they are here.

    Any other thoughts?

  7. #7
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    do you have a fan powered humidifier? IS it set to run with "fan on" or heat only?

  8. #8
    It's a bypass humidifier, no fan.

    Is "adjusting up" the LOW fan speed an option and\or possible solution?

    I ran a Static Pressure Check via the InfinityTouch thermostat.

    I don't know if you can evaluate if my ductwork is good\efficient from the results, but here they are:

    WITH FILTER INSTALLED
    CFM: 906
    Static Pressure .55"
    RPM 899

    Calculated MIN CFM: 300


    WITHOUT FILTER INSTALLED
    CFM: 906
    Static Pressure .45"
    RPM 850

    Calculated MIN CFM: 300

  9. #9
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    No, the low, med, hi speeds are fixed based on equipment airflows and/or soem other logic that Infinity uses. No way to change them.

    0.55" isn't bad. Not outstanding, but not high at all. Max RPM is 1300, so you have a long way to go. I think my upstairs 2 stage Infinity is about the same static wit ha MERV 13 media filter. Downstairs I have a 60k MN7 just like yours. I think low stage is 350CFM, high is 900 CFM and I think medium is therefore around 625. Low fire should be about 330CFM up to I thnk a 45% firing rate, it then ramps up from there.

    I'ts strange that the noise is periodic, not constant. It almost makes me wonder if it's a power quality issue, or some sort of problem with the motor controls. Another person posting on here this Fall had a control board go bad I believe.

    Does the noise correlate with any other change around the house? Something turning on or off?

    My MN7 is absolutely silent standing at hte unit and noise in the ductwork up to maybe 700CFM, then you can hear it a little.

  10. #10
    The current filter is MERV 8.

    The unit is new, installed on 1-31-13.

    It's more or less dead quiet when it is quiet, but when the noise kicks in it wakes me up. The noise is not loud, but the frequency is such that it is really noticeable in a quiet house.

    The only thing I can think of that would be turning on\off at night would be a refrigerator compressor (we have two).

    Is there such a thing as a power conditioning breaker (Square D)? Or is there some other device that could be installed on the furnace to address this issue?

  11. #11
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    You need to make sure that's your problem first. They make whole home power conditoners and ones that you'd wire into an individual circuit. I don;t ebelive any are small enough to simly replace the breaker. It would usually be a seperate box mounted near the panel and wired in series with that circuit.

    I like most have a fridge, a deep freeze and a dehimidifer cycling on and off. I don't suspect that is the cause.

    What has your installer said about the noise?

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