HVAC question-blower motor

Discussion in 'Other Repairs' started by cook, Feb 7, 2007.

  1. cook

    cook New Member

    Messages:
    1,494
    State:
    Plattsburg,Mo.(near K.C.)
    Have a lennox furnace(gas)-no A/C but thermostat is set up for it(4 wire)....was not working well,replaced thermostat today.Main problem is when set to heat/auto......blower hums but won't kick in...spun it by hand and sometimes it will spin...other times not...if set to on(on/auto switch)it kicks right in...start up cap. replaced 2 years ago....shouldn't matter because if turned to 'on' it revolves right away.//did the same before thermostat replacement//

    I could call a repairman(woman),but need to start learning troubleshooting on my own or help from my brothers.

    Any wisecracks or actual suggestions are welcomed:lol:

    signed,shivering in Mo.:cool2: (I wish)
     
  2. troyedm

    troyedm New Member

    Messages:
    83
    State:
    edmond oklahoma
    there is a temp switch on the outside of the flame box. it is wired to turn on when your furnace reaches a certain temp. ( this prevents cold air circulating while the furnace gets up to temp) when you turn the fan from auto, to on you bypass that temp switch. if you trace your wiring from the fan motor back you should find the temp switch. you can purchase the temp switch, maybe at lowes. make sure you turn the power off to the furnace unit when you change the switch.
     

  3. cat tamer

    cat tamer New Member

    Messages:
    694
    State:
    MO
    If the blower hums with a call for heat then it is not a control problem such as limit or a fan switch, the problem would either be a faulty run capacitor or a faulty winding in the motor or the bearing in the motor are binding, even though you replaced the capacitor a couple years ago doesent matter, the new caps keep getting smaller physicaly and don't last as long as some of the old style.
    I would change the capacitor and make sure it matches the motor requirment on the info sticker on the motor and if that does not fix it then it is probably the motor.
    lennox has some small framed motors so if you do buy a motor make sure it is compatible.
    kirk
     
  4. cat tamer

    cat tamer New Member

    Messages:
    694
    State:
    MO
    Jon I reread your post and missed the fact that it run's fine when turned to on, as a rule when you switch the stat to on on the older furnaces the fan relay switches on high speed and when the fan is brought on, in the call for heat mode it brings on a slower speed, with that said it appears that the slower speed winding is at fault, if you have another speed lead that you can switch to, that could save you from buying a new motor and if all else fails use the high speed that does work for both.
     
  5. cook

    cook New Member

    Messages:
    1,494
    State:
    Plattsburg,Mo.(near K.C.)
    Well,got worse and worse...I finally pulled the motor and had it checked out.Bearings were going bad.Replaced it for 80$ not to bad...hardest part was laying on my back in a 2x2 foot area reinstalling it...had to hold a 50# unit over my head with one hand and start the bolts with another,a third hand would have been handy:lol: