Furnace and heat pump fan motors

can be easy to replace and repair.

    I get lots and lots of inquiries about fan motors and what to do to replace them when they fail.
 Most fan motors on residential equipment are of a standard size known as 48 Frame (5-5/8 inches diameter). A larger size that is used is a size known as 56 Frame (6-1/2 inches diameter). The power of these motors range from about 1/8 th. of a horsepower to 3/4 horsepower and everything in between. Most common powers are 1/6, 1/5, 1/4, 1/3, 1/2, 3/4, and 1.

    The most common RPM is 1200 (1050 or 1075) also 900 (850, 825) and 1550 are used too. Most motors are single speed but can have as many as 4 speeds (3 is typical for direct drive indoor blowers on most furnaces). On direct drive blowers usually high speed is used for air-conditioning and lower speeds are used for heating or air circulation.

    Wiring colors for most motors are White = Common, Black = High, Yellow = Medium, Blue = Medium Low, Red = Low. Brown w/white tracer is for the run capacitor the same as white. Brown is for the run capacitor. If you can place the run capacitor in the equipment cabinet use the brown with the white tracer and tape off the white wire because both brown wires have 1/4" quick connectors on them. We know of an instance where someone drilled a hole in their coil just so they could fish that fourth wire instead of just using three wires (a very expensive wire).

    Most fan motors have bronze sleeve bearings but can be ordered with ball bearings. Sleeve bearings will last many years but a ball bearing motor can last even longer (decades) especially in severe applications where the equipment runs continuously. Most motors with sleeve bearings will have a set of removable plugs where you can oil the motor. I recommend a few drops of SAE 20W oil NON DETERGENT (3 in 1 in the BLUE not the RED can) every year. Some OEM  (original equipment manufacturer) motors do not have oil ports. If you replace a motor and it has oil ports try to place them between 10 o'clock and 2 o'clock. There is a device available that will extend the oil ports so you can reach the rear port on direct drive blowers. NEVER use WD 40 to lubricate a motor since it has little or no lubricating properties for bearings and will wash out the heavier oil. But it is good for getting stuck shafts off.

    There are a handful of manufacturers such as General Electric, A.O Smith, Marathon, Magnetek, Emerson, Century, Universal, Fasco and Baldor. Any of these manufacture's products will work just as good as another (in my opinion). I have used just about all of the different motor manufactures and have not noticed any difference in performance or life. However some OEM (original equipment manufacturer) motors will have a thrust bearing so when used in vertical shaft up they will tend to last longer than some replacement motors.

    To replace a motor it is necessary to remove the blower wheel or fan blade from the motor. If the fan or blower does not come right off (sometimes it will) the best way to do this is to use a puller that will pull the hub off of the shaft. DO NOT use a hammer to try to drive the shaft though the hub, you will just distort the shaft to the point where you will have saw the shaft off or just buy a replacement fan blade for your new motor if the fan blade is in bad shape.

    If you have an electrical failure where the motor smokes or stinks it is probably done. If the motor gets hot it will usually shut off because it has a thermostat inside to protect it. A motor that was normally working ok and suddenly gets hot may have a bad run capacitor. The run capacitor is a round or flat silver can rated at 5 to 7.5 Mfd (micro farads) for most 208-230 volt motors. To test a run capacitor use this test chart NEVER an ohm meter. If this is the case you can usually just replace the capacitor and your problems may go away. Only single phase motors have run capacitors, three phase motors do not. Some motors for belt drive applications will have a start capacitor but no run capacitor. Some larger motors will have both.

    When you replace a motor keep in mind that fans for outdoor use will usually be sealed up and motors for indoor use will be open. An open motor can have a higher rating than one that is closed because of the air flowing over the windings. As far as ratings are concerned do not replace a motor with one of a smaller horsepower ratting but know that a larger motor will waste energy because motors are most efficient when loaded to 80- 90%. Warning: some OEM (original equipment manufacture) motors will have lower name plate ratings that the actual ratting, EX: a 1/2 HP motor may actually be 3/4. If your fan blade is 24 inches or larger you should use a 900 (850, 825) rpm motor.

Related Pages:
    Wiring colors.
    Electric furnace trouble-shooting.
    Fan Blower Motor controls.
    Motor Run Capacitor test chart.
    Problem solving.
    More F.A.Q.
    More definitions.
    Gas burner system page.
    Oil heat page.
    Heat pump repair page.
    Heat pump defrost cycle.
    What is a combustion blower?


  1. Blower: usually a squirrel cage centrtrifigal air moving device. Will move large volumes of air relatively quiet. Will use less energy with more back pressure.
  2. Fan: a paddle type air moving device used where noise is not a major consideration. Will use more energy with more back pressure.
  3. Combustion blower: A blower used on high efficiency furnaces or oil burners to move combustion air. usually 1/20 to 1/6  horsepower.
  4. OEM: Original equipment manufacturer.
  5. Horsepower: 746 watts
  6. RPM: revolutions per minute.
  7. Service factor: the extent to which a motor can be safely overloaded beyond its name plate ratting without over heating.
  8. Air over horsepower: The rating of a motor assuming air flow through the windings usually as a result of the air moving device.
  9. SAE: Society of Automotive Engineers.
    This page will be updated soon
 Good Luck Scott
If your heat pump forms ice outside in the heat mode click here.
If your air conditioner or heat pump ices up in the cooling mode click here.
If you have water leaking problems click here to solve it.
For other heat pump problems click here.
For other heating system problems click here.
 Any other questions feel free to contact us by any of the means below. good luck Scott.
    If you were looking for Ice Machine repairs click here.

Written By:  Scott Meenen N3SJH of:
Specializing in Mechanical, Controls and Electrical Modifications Of
Heating, Air conditioning, Refrigeration, Cold storage,
Ice Production and Food preservation.
Anything having to do with Heat and Energy.
Serving MD, DC, and Northern VA.
Contact us by pager: 1-877-467-2914
Here at G&S Mechanical we can repair or improve your domestic (household) hot water systems. Whether you system is electric, gas, oil, heat pump,

Page us by e-mail 4103560613.3732505@pagenet.net 240Chrs max.

Email us at: jsmeenen@toad.net

                 This text written by: Scott Meenen * G & S Mechanical

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