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  1. #1
    Join Date
    Sep 2004

    Downflow Miller furnace problem.

    A downflow Miller (CMF100) furnace is installed in a manufacturered home. The owner is south for the winter and the thermostat is set low. The furnace is cycling and not heating.
    Here is what I think is happening - the fan is at the top (inlet) and the fan control is between the fan and the burner. The burner starts and when the fan-start temp is reached the fan starts. The fan blows cold air over the control which drops back down low enough to stop the fan.
    Anyone seen this problem?
    I can set the fan stop lower and/or the furnace start higher ond/or raise the temperature in the house (so the return air is not so cold).?.

  2. #2
    Join Date
    May 2006

    Miller Downflow Furnace Problem

    i own the sister furance to that model and it uses the honeywell fan manager with the silver disk i dont rember the cut in and cut out temps exactly but i do know nordyne aka miller has known problem when you keep the house under 59 degrees that the fan will cycle on and off while the burner keeps heating the heat ex and will do so untill the air comeing in to the blower intake is over 62 degrees as i have to keep my unit at 62 and during the day i put it up to 68 and if its really cold out side it does it now and then all the techs i have spoken to say its normal.
    i strongly recommed you donot mess with the settings on the fan manager dial.
    if you dont do them exactly as the printed directions on the dial say you can peramanalty damage the fan manager .
    this cycleing accorinding to the maker will not harm the unit.
    but it is annoying at times
    some say lower the fan speed but doing that can cause poor air flow and bills to match.
    if you have any doughts call a pro and have them look at it .

  3. #3
    Join Date
    Jan 2007
    Sounds like you are right when you say return air is too cold. I have run into that a few times with other systems. I wouldn't mess with changing the fan control settings if they are adjustable. Do you mean that the house is not ever getting up to the setpoint temp.? If so, then maybe turn the fan on to run constantly.

  4. #4
    Join Date
    May 2006

    Downflow Miller Fruance Problem

    hi no it heats the house fine but if you dont keep youre home at 62 and i dont when i go to bed i like it cool i set it at 59 or 60 it will cycle the fan a few times untill the air comeing in to the blower gets over 62 .
    i talked to miller again for you to day and its a normal operation of the furance for it to do what its doing .
    just make sure the blower motor openings are free of dust and lint and make sure the foam filter in the door is clean .
    i vacuim mine out and then wash it carefully in the tub let it dry then put it back in and fire the unit up the book says every 30 days i do it less often as my home is very clean.
    have any of yo techs had any problems with the blowers going in the miller line ?
    and i know you cant give priceing on the site but can i ask what the range is for a CFM or CMF 80PO miller furance for a blower motor.

  5. #5
    Join Date
    Aug 2004
    Kentucky, Michigan, Ohio, Arizona, Colorado, Nevada, and Califormia


    Blower motor RPM is defined by application. Static pressure, system requirements, desired CFM all have bearing. R/A temperature can have an effect on a honeywell fan/limit.
    More importantly, restricted supply, restricted return, dirty components, improper wiring, improper part replacement, restrictive filters and more have a bearing on furnace performance. If left to cycle on limit too long, it's a fire/C.o. hazard. Since you took the time to post here, take the time to call a professional.
    "Surprised ?! If I woke up tomorrow with my head sewn to the carpet, I wouldn't be more surprised."
    Clark Griswold

  6. #6
    Join Date
    Aug 2002
    manitowoc wisconsin
    It is normal operation.most furnaces should not be used under 60 deg.low temps can cause sooting,stress to heat exchanger, not run the unit fan below minimum temperature it could damage the unit.
    Take your time & do it right!

  7. #7
    Join Date
    May 2006

    for ira miller downflow furance problem

    ira he is not talking about the burner or messing with the fan settings and what not he is talking about the blower cycleing on the lower temp setting.
    its a known problem for thise model miller furances.
    read the first post before you jump his crap.

  8. #8
    Join Date
    Mar 2005
    burlington county n.j.
    most furnaces controlled by a fan-limit switch will cycle the blower with very low return air temps.

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