Diagnosing a faulty blower motor...

If you suspect your motor is bad, you should check to make sure before you replace it. Begin diagnosis by shutting off the power to the furnace. Then, try to spin the blower by hand.

If it will not spin freely, check to see if it has oil ports on the blower. If it has oil ports, you should add a few drops of oil to see if it helps the motor to spin freely. If there are no ports or it still does not spin freely after adding oil, the motor should be replaced.

If the blower spins freely, feel the motor to see if it is hot. If the motor is hot to the touch, allow it to cool. Check all the wire connections to ensure they are tight, check the run capacitor and replace it as necessary.

Then you can check to see if the motor works properly. Turn the power back on and turn the fan on at the thermostat. If the blower does not start or fails to get up to full speed, shut the power back off to the unit and continue with furnace blower replacement.

Removing the old motor...

To begin the removal of the old motor, you should write down the motor wire colors and where they are connected. Then you can disconnect them. On newer furnaces they will be connected to the furnace control board by spade connectors. Most older furnaces have a wiring control box with a relay and the wire connections.

Next, you should remove the bolts or nuts that hold the blower assembly in the furnace. This is typically two nuts or bolts towards the front of the blower assembly.Then, you can slide the blower assembly out of the furnace.

To remove the motor from the blower assembly, start by loosening the set screw that attaches the wheel to the motor. Then remove the motor mounting bolts which hold the motor to the housing. You should be able to pull the motor out now.

After you have the motor out, you should remove the mounting bracket from the motor. Be careful to note the orientation of the motor in he bracket.

**NOTE** Some older units have the mounting brackets built into the motor. If this is the case, you will need to purchase the exact replacement or a motor and an adapter kit.

Furnace Blower Replacement, Selecting a replacement motor...

Now that you have the motor out, the next step in furnace blower replacement is selecting the proper replacement. 

 If you are unable to find the exact replacement, you can usually use a universal replacement. Here is what you should look for and match:

1. type of drive( direct or belt)

2. motor diameter in inches (3.3, 5, 5.5, 6.5)

3. voltage (115,208-230,460)

4. horsepower (1/4, 1/3, 1/2, 3/4, 1)

5. speed in rpm

6. number of speeds available

7. direction of rotation (it is best to get a reversible one)

8. mounting method (typically a belly band)

9. size of run capacitor required

Installing the new motor...

To put the motor back in, simply reverse the removal procedure.
Some key things to ensure proper installation are:

1. Before you secure the wheel to the motor, ensure that the wheel is centered in the housing.

2. Ensure that you have selected the proper rotation direction.

3. Any unused motor leads should be individually isolated using wire nuts and/or electrical tape.

4. It is a good idea to replace the run capacitor any time a motor is replaced.

5. After you have finished, you should complete your furnace blower replacement by checking for normal operation. Listen for noises and check to ensure that air is coming out of the supply registers.

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