How to Build a Gas Furnace Blower

What You'll Need
Notebook and pencil
Replacement furnace motor blower
Replacement run capacitor

If you have looked over your gas furnace blower and decided that it's time for a new one, you can do the work yourself. 

Step 1: Check 

You might think your furnace motor is no longer useful, but check it first to be sure. Shut off the power that goes to the furnace. Then try spinning the blower by hand. If it will not spin, add a few drops of oil to the oil ports. If that doesn't do the trick, then you should rebuild your blower. 

Step 2: Remove Motor Wires 

Write down the colors of the motor wires and where they are connected before you disconnect them. In newer furnaces, you'll find them attached by spade connectors to the furnace control board. In older furnaces, you'll find a wiring control box with a relay and wire connections. 

Step 3: Remove Nuts and Bolts 

Remove the nuts and bolts that keep the blower assembly in the furnace. The nuts and bolts are generally near the front of the assembly; there are most likely two of them. You can take the blower assembly out of the furnace once you've removed the nuts and bolts. 

Step 4: Remove the Motor from the Blower Assembly 

Remove the motor from the blower assembly by loosening the setscrew. Take out the motor mounting bolts. Pull the motor out. 

Step 5: Remove the Mounting Bracket 

Once the motor is out, remove the mounting bracket. Make sure you pay attention to where it was positioned before you take it out. However, some older models have their mounting brackets built right into the motor. If that's the case, you'll have to buy a substitute that is exactly the same, or a motor and adapter kit. 

Step 6: Select the Right Replacement 

You'll want to make sure you get the correct replacement for your furnace blower. You can find the exact replacement by finding the manufacturer number on your old one. However, you can also get a universal replacement. There are some things to look for if you are going to follow that route. Look for the following and match:

  • Which drive is it? Belt or direct?
  • What is the diameter of the motor in inches? (3.3, 5, 5.5 or 6.5)
  • What is the voltage? (115, 208-230 or 460)
  • What is the horsepower?
  • What is the speed in RPM?
  • What are the number of speeds available?
  • What types of directions of rotation are available (reversible is best)?
  • What is the mounting method (commonly belly band)? 
  • What size of run capacitor is required?

Step 7: Put the Motor Back

To put it back in, do the reverse of what you did to take the motor out. However, take note of a few things for proper installation:

  • Make sure the wheel is centered in the housing before you secure it to the motor.
  • Make sure you've chosen the correct rotation direction.
  • If you have any unused motor leads, isolate them individually using wire nuts and electrical tape.
  • If you replace the motor, it's recommended to replace the run capacitor.
  • Once you're done, check to make sure everything is running properly.