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  1. #1
    Join Date
    Jan 2005
    Posts
    20

    Question fan speed options

    This isn't DIY, I'm trying to find a pro that can do this but my questions so far to locals seem to point to this not being possible unless we replace the furnance. So I figured i would ping this forum for thoughts.

    We just had a central ac unit replaced and are happy with the install / pricing / workmanship. Part of the install happened to be the need to adjust the fan speed setting for the new ac unit. (old an new units are different tonnages)

    The existing furnance is a trane xl 90 100k btu, it has a 4 speed blower fan.

    So now the blower fan is adjusted for the heating (slot 4 high speed) and adjusted for the ac (slot 3 med high speed). All works as exspected.

    But...
    In our home we have the blower fan run 24/7 in order to maintain a more level temperature (2 story with basement). With the new settings on the blower fan the fan noise is much louder (as exspected since it is set higher).

    Honeywell Chronotherm IV Plus is the tstat

    My question:
    With the above setup is it possible to have the fan step down to one of the other 2 lower speeds (like slot 1 or 2)when the fan is on but there is no call for heat or cooling? If not with the above setup would it be possible to swap out something cheaper then a furnance and get the intended result?

  2. #2
    Join Date
    May 2007
    Location
    Alabama
    Posts
    909
    It can be done if your contractor is good at creating circuits.

  3. #3
    Join Date
    Sep 2006
    Posts
    1,253
    If you have noise that is unacceptable then you probably have sizing problems somewhere in your duct system. The problem isn't the fan speed, it is the duct work/sizing. Your system may not be moving the air that it needs because of these issues.

    Before you spend the money having someone set it up to run in a lower speed you should have the duct work fully evaluated and corrected. Undersized duct work can shorten the life of the equipment. The noise is just the symptom not the issue.

  4. #4
    Join Date
    Jan 2005
    Posts
    20
    thanks Bamacool for the quick reply

    So it sounds like I need to talk to my installer and find out if they are able to 'create a circuit' for a new fan speed. And if they are not able to I should call someone who is familar with that request.

    Thanks again for the info, I'll start calling

  5. #5
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by mchild View Post
    If you have noise that is unacceptable then you probably have sizing problems somewhere in your duct system. The problem isn't the fan speed, it is the duct work/sizing. Your system may not be moving the air that it needs because of these issues.

    Before you spend the money having someone set it up to run in a lower speed you should have the duct work fully evaluated and corrected. Undersized duct work can shorten the life of the equipment. The noise is just the symptom not the issue.
    stieny,

    Based on times posted,I think you misssed this one.

    might want to consider the advise.

    Speeds between old and new unit mean very litlle,it's all based on the fan data chart of the new one,as to what speed is needed.

    did you go larger or smaller with the new one?Model numbers for both would help.

  6. #6
    Join Date
    Mar 2003
    Posts
    7,326
    I am guessing your new unit is larger than the old one? At any rate it shouldbe pretty easy for a competant mechanic to add relay logic to make the switch occur for you. It may even be able to be done on the board without relay logic. If your guy cannot do it I would be shocked, unless of course he did this project "on the side" in which case I completely get it.

  7. #7
    Join Date
    Jan 2005
    Posts
    20
    To the question of old vs. new blower:
    The installer was able to locate a new motor with the same specifications as the previous one. Motor size / hp, the rpm's at the various speeds were not 'exact' but within a very small difference. From memory the differences were sub 5%. I don't have the part numbers on hand but I do recall the installer showing me the two fans side by side and calling out how near 'exact' they were.

    To the question of how it was installed:
    Definately not on the side. We went through a reputable dealer and their crew was all on the clock. Absolutely not a side job, this isn't something I wanted to save a buck on.


    I believe my issue is that we (wife and I) have gotten very used to having a blower fan with which is completely silent and now that we have some noise we would like it removed if possible. While the installer was present he put the fan on the lowest setting and it worked as intended 'silent'. The issue being that the furnance doesn't appear to support that configuration.

    I'll need to find a local crew that has the ability to add this feature. Much appreciated on the advice.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,097
    Is it the same size furnac BTU wise as the old furnace?
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  9. #9
    Join Date
    Sep 2006
    Posts
    1,253
    Quote Originally Posted by steiny View Post
    To the question of old vs. new blower:
    The installer was able to locate a new motor with the same specifications as the previous one. Motor size / hp, the rpm's at the various speeds were not 'exact' but within a very small difference. From memory the differences were sub 5%. I don't have the part numbers on hand but I do recall the installer showing me the two fans side by side and calling out how near 'exact' they were.

    To the question of how it was installed:
    Definately not on the side. We went through a reputable dealer and their crew was all on the clock. Absolutely not a side job, this isn't something I wanted to save a buck on.


    I believe my issue is that we (wife and I) have gotten very used to having a blower fan with which is completely silent and now that we have some noise we would like it removed if possible. While the installer was present he put the fan on the lowest setting and it worked as intended 'silent'. The issue being that the furnance doesn't appear to support that configuration.

    I'll need to find a local crew that has the ability to add this feature. Much appreciated on the advice.
    While the blowers may have seemed very similar they may be more different than meets the eye with regard to the air being moved.

    If you could provide the model number of furnace, the air flow for each speed could be checked. It may be that the heat speed on tap 4 is too high. Most units com from the factory set to high and the installer leaves it there.

    The noise is most likely from the unit trying to push too much air through too small a space. With four speed taps you may be able to resolve your issue with custom engineering. Measuring your temp rise would be something to have your contractor do and will help tell you if you can drop the fan speed.

  10. #10
    Join Date
    Jan 2005
    Posts
    20
    furnance model is TUC1008960A0


    furnance hasn't changed but a new ac unit was installed, the new ac is larger and required an adjustment of the fan speeds to support the added tonnage

  11. #11
    Join Date
    Sep 2006
    Posts
    1,253
    Quote Originally Posted by steiny View Post
    furnance model is TUC1008960A0


    furnance hasn't changed but a new ac unit was installed, the new ac is larger and required an adjustment of the fan speeds to support the added tonnage
    What is the a/c size?

  12. #12
    Join Date
    Dec 2007
    Location
    Cedar Grove, Wi-Sheboygan
    Posts
    1,582
    So you have a 4 speed tap settings for your furnace, one tap for heating and one for cooling, and you say you have replaced the existing OD unit with a larger one thus leaving you with undersized duct work that will not support the full amount of air needed for the new OD unit without creating noise from your registers. I think you maybe able to leave your tap speed for cooling on high and put a bypass in the duct work to allow the extra forced air to return into your return drop to reduce the excess static/back pressure. I think if you do not have the proper CFM's for the larger AC your likely to cause the ID coil to freeze up creating more prolems for you I had a 20 yr old Tempstar that was set-up as your furnace is with the tapped speeds and I recall being able to set the speeds for heating on med, cooling on med high, and fan on low in continuous run without any problems, and so I am wondering why your not able to do the same

  13. #13
    Join Date
    Jan 2005
    Posts
    20
    a/c is 4 ton

    I'm looking for exactly as DanW13 stated. Use 1 tap for heat, 1 tap for ac and 1 tap for fan.

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