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  1. #1
    Join Date
    Dec 2001
    Location
    Cartersville Ga
    Posts
    1,035
    one of our techs went on a call today. 80% lennox gas furnace, less than 1 yr old, 5 ton drive. i assume this is a 3/4 hp motor. he says it is pulling 12 amps while running, 22 peak at startup. also says tag on unit does not indicate motor size or amp draw, but 12 amp max circuit, sounds high to me. return comes in on both sides of unit, clean filters and blower wheel.

    should i order a motor? 12 amps (hi speed) sounds high to me
    In the land of the blind the one eyed man is King! semper fi

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,290
    Did he check the run cap?
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #3
    Join Date
    Jul 2004
    Location
    West TN
    Posts
    983
    CHeck your CFM

    If the resistance of the duct is real low (very easy to move the air), then the blower will react much like you
    riding downhill on a ten speed bicycle in 1st gear.

    The blower amps tracks pretty close to total CFM.
    If your CFM is correct, run capacitor is good, and voltage is OK, then I'd suspect a bad motor.
    If you checked your static pressures and they line up ok on the cfm chart, then check the CFM with an alternate method to make sure. I use a velometer and return grille Ak factor. If all else fails, check the CFM using a heat rise.

    I'd also check bearing condition and temp of motor after its run a while (forget temp if CFM is not right though)

    What was the complaint the tech was sent to check for? (out of curiosity)

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,242

    Question Specs

    Originally posted by hvac4u
    i assume this is a 3/4 hp motor. he says it is pulling 12 amps while running, 22 peak at startup.

    should i order a motor?
    Sure and make it
    a 2 HP .. BIGGER IS better.
    TWICE the HP will get you HALF THE AMPS.

    Just where you need to be ! !! !!! ?
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #5
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,024
    Did he have the blower door on?

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