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  1. #1
    Join Date
    Jul 2007
    Posts
    65

    Capacitor check on furnace.

    I had looked at furnace with run cap for blower, unit was off on high limit. Did cap test and had 1.2 micro farads(cap rated for 5mfd) Cap wasnt bulged but my question is at 1.2 can I assume cap is at fault not blower? Even though it is not entirely open. Blower was hot. Didnt have cap in van at time so I will have to go back. Tested limit, when things cooled off and it was closed.

  2. #2
    Join Date
    Feb 2010
    Location
    Calgary, Alberta
    Posts
    1,153
    Probably.
    See how it runs with the new cap, you might be too late!

  3. #3
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    yep.... change it all will be good..... well done lots of tecs would of changed a perfectly good motor... 1.2 is not close to 5 it should work.....
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  4. #4
    Join Date
    Dec 2011
    Location
    somewhere between here and there
    Posts
    478
    next question....

    why do you not have a blower cap on your truck????


    Please, Please Please......keep the Factory Smoke in the Wires!!!!!


    Is it Rum'Oclock yet???

  5. #5
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    good point.....
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  6. #6
    Join Date
    Jul 2007
    Posts
    65
    Okay thanks, and agrred I do need to get some more van stock.

  7. #7
    Join Date
    Mar 2004
    Location
    SE Michigan
    Posts
    18,223
    Depending on the age/condition of the motor, it may not be a bad idea to replace both the cap and motor. Customers get pissy when you have to go back a few months later to replace the motor. .02
    To put the world in order, we must first put the nation in order; to put the nation in order, we must put the family in order; to put the family in order, we must cultivate our personal life; and to cultivate our personal life, we must first set our hearts right.
    -- Confucius

  8. #8
    Join Date
    Sep 2012
    Location
    NW Louisiana
    Posts
    159
    1.2 mfd vs 5 mfd? This is off 76% of a 5 mfd cap. Most caps are (+/-) 5%-10% tolerance. Change is good!

    CT

  9. #9
    Join Date
    Sep 2012
    Location
    Hebderson Ky
    Posts
    55
    I would check your amp draw on your motor after replacing capacitor to insure condition of the motor.

  10. #10
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,122
    Quote Originally Posted by nsula_country View Post
    Most caps are (+/-) 5%-10% tolerance.
    Someone has been doing his homework, you are correct. I have seen numerous post here in my past years, that say "motors" have a 5%-10% tolerance. I have often wondered if the caps have a tolerance percentage, does this mean that the motor mfg. would say it ok for their motor designed for a 10 mfd. cap, to run at 9 mfd.? Maybe bypass a call to the distributor, straight to the mfg. would get you the correct answer, straight from the horse's mouth.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

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  11. #11
    Join Date
    Sep 2012
    Location
    NW Louisiana
    Posts
    159
    Quote Originally Posted by Mr Bill View Post
    Someone has been doing his homework, you are correct. I have seen numerous post here in my past years, that say "motors" have a 5%-10% tolerance. I have often wondered if the caps have a tolerance percentage, does this mean that the motor mfg. would say it ok for their motor designed for a 10 mfd. cap, to run at 9 mfd.? Maybe bypass a call to the distributor, straight to the mfg. would get you the correct answer, straight from the horse's mouth.
    I'm unsure about the motors, but can investigate. Most run caps are (+/-) 10% tolerance. So if a motor requires a 10 mfd cap, the cap should read 9 mfd-11 mfd (10%). The motor designers should have this variance factored into the motor design. I would say it would be better to oversize a cap than to undersize it, but not more than 1 size up and only until the proper replacement can be installed.

    Reasons:

    Efficiency - A capacitor attempts to correct a poor Power Factor by adding Capacitance Reactance. Since a compressor or fan motor is an inductive device with Inductive Reactance, a capacitor will largely zero the reactances, resulting in a compressor or fan motor that runs cooler and uses less electricity. Oversizing or Undersizing screws with the Power Factor on a RUN capacitor.

    Rules for Capacitor Replacement:

    -Voltage must be EQUAL TO or GREATER than the cap being changed (ie, 370V)
    -Start Cap must be (+/-) 20% of mfd
    -Run Cap must be (+/-) 10% of mfd
    -If the Start Cap is UNDERSIZED, the motor might not start.
    -If the Start Cap is OVERSIZED, the high start current might burn out the start winding (Hard Start Kit ???).
    -If the Run Cap is incorrectly sized, the Power Factor will suffer, resulting in lower efficiency, higher operating costs, and possible motor damage.

    A failing cap can:
    --reduce the speed of the motor, which
    --increases the motor’s temperature
    --causes bearing wear and insulation breakdown
    -- increases overall noise

    Basically the capacitor values posted on nameplates are engineered to be optimum for peak performance. replace with like part!

    Run capacitors are there to correct the single-phase power factor. Three-phase is nearly perfect at 1.00 power factor, but sometimes capacitor banks are used to balance power factor in imbalanced systems.

    Good luck!

    CT

  12. #12
    Join Date
    Sep 2012
    Location
    Texas
    Posts
    23
    Quote Originally Posted by Hwolfe View Post
    I would check your amp draw on your motor after replacing capacitor to insure condition of the motor.
    ^This

  13. #13
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,596
    Quote Originally Posted by B-Tech View Post
    ^This
    X3

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