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Furnace, Air Conditioning Motor Education

Before you attempt to work on, or replace your direct drive motor in any central furnace, heat pump, air handler or air conditioner please read this article as it may well save you from making costly mistakes and may well keep you from personal injury or damage to your equipment. Also note: if your motor uses a belt do not order a direct drive motor, instead see our belt drive motors.

This article is being written by a H.V.A.C. Technician with over 28 years of field experience. As such we will try to talk in plain language wherever we can.

120 VOLT GAS FURNACES. WITH DIRECT DRIVE MOTOR. SEE HEAT PUMPS, AIR CONDITIONERS, ELECTRIC FURNACES AND AIR HANDLERS AT BOTTOM OF THIS PAGE.

THESE GUIDELINES DO NOT APPLY TO VARIABLE SPEED EQUIPMENT.

  1. When you have to remove a bad direct drive motor from your furnace, the first thing that you have to do is be sure the 120 Volt power is off! There is USUALLY a service switch near the furnace that can be shut off, but we suggest shutting the power off at the main breaker panel.
  2. The blower assembly will need to be removed from the furnace. Most older furnaces have a simpler arrangement that the motor wires go to known as a fan center. Some others use a relay to accomplish this, while the newer furnaces use a Printed Circuit Board that the motor leads attach to. Whatever system you have, be sure to identify all the motor wires as to color and where they went before you remove any wires. Also if there is a separate run capacitor on or being used by the motor, this capacitor must be discharged by shorting the capacitor leads together with an insulated screwdriver. IF YOU REALLY DON'T HAVE THE MAIN 120 VOLT POWER OFF, YOU WILL PROBABLY GET A NASTY SHOCK!
  3. Once the blower assembly is sitting on the floor, notice there is a bracket of some kind holding the motor to the blower housing. If you turn the assembly over you will also see there is either a set screw or some other holding fastener holding the blower wheel to the motor shaft. This set screw is located in what is referred to as the " Hub. The rotation blower wheels are while viewing the Hub. "While looking at the shaft you should measure the shaft size as most furnaces use a 1/2" shaft on the motor but some use larger shafts!
  4. In a perfect world removing the set screw that holds the wheel and the bolts or screws that hold the mounting bracket to the housing will let the motor drop out of the blower wheel. Note we said a " Perfect World "!!! The real world says that MANY times the shaft will be rusted or frozen in some way and will not budge! When this happens, a service technician would spray WD40 or Liquid Wrench on the shaft and use a brass drift and a hammer on the end of the shaft to drive it out of the blower wheel. If this doesn't work the service person might have to use a specialty puller to get a wheel or AC fan motor off. To see one click this link Fan and Blower Wheel Puller. Even using these methods, some motors, especially ones located outside as in heat pumps, air conditioners or package units will absolutely not come loose. When this happens the technician may often, need to try to get a new wheel and literally have to cut the wheel and shaft out. On belt drive blowers, sometimes the entire shaft and bearings may need replacement along with a new pulley or sheave which is on both the motor and blower wheel. It will be important to get the same sizes that you took off if this happens.
  5. If we manage to actually get the motor out, replacement pf the motor amounts to getting a replacement that matches the existing motor, assuming that motor was correct to begin with! Many pieces of equipment have had their motors changed by home owners or handy men who don't install the correct horsepower, R.P.M. or even voltage which will lead to a failure. Bear in mind if air conditioning has been added to a Heat Only furnace, chances are good that your original motor is not big enough now! If this is the case and you need more air flow, go back to our category page and look at the High Speed 1,625 R.P.M. Motors. Installing just a larger horsepower motor may solve air flow problems, however, in our experience it is much better to go with the 1,625 R.P.M. Motors when you are trying to help air flow problems!
  6. Pay careful attention to how your existing motor mounts, there are resilient mounts that have rubber cups on the end bells of the motor, there are also stud mounts , but most use a belly band mount around the motor. Manufacturer's use different diameters, different R.P.M's and different Horsepower motors. Installing the wrong motor will cause damage eventually, if not immediately! Our motors have studs and black rubber cups around the end bell. If the studs aren't needed they can be cut off if they interfere with the blower wheel.

Carrier Condenser Fan Motors as used in the older Carrier Round Condensers have 3 ears welded to the motor for mounting purposes and is 5 5/8" in diameter. While our motors are 5 5/8" in diameter, they will not have these mounting ears! This is just ONE of the things you must look into BEFORE ordering! Some furnace motors do the same sort of things in their mounting, while others use different horsepower or R.P.M. ratings! We sometimes ask for a digital picture to help find the right motor for you. But it is your responsibility to read the information on the actual motor you are replacing. Please don't assume we can find the correct motor with out dated furnaces and only partial model and serial numbers from the equipment.

  1. When installing the new motor, care must be taken to be sure the wheel is lined up in the center of the blower housing. Tighten the set screw on the FLAT SPOT provided on the motor shaft. Spin the wheel to be sure it doesn't hit any where.
  2. All the motors we sell are P.S.C. (Permanent Slit Capacitor) and have to use a run capacitor, please order our capacitors separately. The PSC Motors are much more efficient in operation and will be cheaper to run over the long haul, as well as lasting much longer than the cheaper shaded pole varieties provided by the manufacturer's. Most of our motors are 5 5/8" in diameter, and are electrically reversible.
  3. If you have an old unit chances are good that the new replacement motor will use different color codes, wiring diagrams, or mounting and will require you or someone skilled enough to be able to deal with these changes! Even motors directly from the manufacturer of the equipment may be different as far as the wiring goes, than what you have!

HEAT PUMPS, AIR CONDITIONERS, ELECTRIC FURNACES AND AIR HANDLERS

Heat Pumps, Air Conditioners, Electric Furnaces and Air Handlers all use 208/230 Volt motors.

While the PHYSICAL installation parameters may be similar, the wiring of a 230 Volt motor will not be the same and should only be done by persons qualified to do so for obvious safety reasons! If you are qualified, please refer to our Category Page for the correct motor and capacitor. If you aren't qualified you can still save big money by getting your own parts, and let an H.V.A.C. Company do the work!

Before ordering any motor be sure to check the name plate on your present motor for the following.

  • Horsepower rating: While it is alright and probably more desirable to go another size bigger, you may need to adjust the blower speed taps to a lower speed to keep the temperature rise/drop through the furnace and air conditioning coil within manufacturers recommendations ( see the plate in your furnace ).
  • R.P.M. (Revolutions Per Minute). Keep this the same as what you have unless you are PURPOSELY trying to achieve more air flow as with a 1,625 R.P.M. motor. Bear in mind that some manufacturers such as Lennox use 825 R.P.M. motors. Using a 1,075 or 1,625 R.P.M motor in this case, will lead to more noise and probably burning out the new motor unless you also oversize the new motor.
  • Check the Phase. Most residential units will use a Phase1, however, rooftop or package Heat Pumps used for commercial buildings may have Phase 3 motors! Be sure to verify this and voltage before ordering!
  • Check the voltage that the motor uses, 99% of all furnaces use 115 or 120 volt motors, however, some REALLY old furnaces have been known to use 230 volt motors. Likewise commercial package units might use 230 volt motors especially on package Heat Pumps!
  • Check the diameter and the shaft size of your present motor.
  • Will your present bracket fit the new motor or will you need a new bracket?
  • Rotation: All our motors are reversible, others suppliers may not be!

 

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