If your furnace blower is no longer pushing heated air through the registers and vents, then it is likely the blower motor has failed and needs replacing. Fortunately, replacing the blower motor is a fairly easy repair for most homeowners, and it only requires the use of a few simple hand tools. Below is a step-by-step procedure for removing the old blower motor and replacing it with a new one:
1. Disconnect electrical power to the furnace - Before you begin disassembling the furnace and attempt to remove the blower motor, it is critical to disconnect the unit from your home's electrical supply. Some furnaces are powered by 240 volts AC, and accidental contact with current at this level could be deadly. Even touching a live circuit inside a 120 volt AC furnaces can be dangerous, so don't take any chances by merely turning off the thermostat. Instead, turn off the furnace main power switch located next to the unit, or disconnect power at your home's circuit breaker panel.
2. Remove the appropriate access cover - Your furnace will likely have two access covers, one of which covers the burners or heating elements, and the other that covers the blower fan and motor. Remove the appropriate cover using a screwdriver or nutdriver or by unfastening the latches that hold it in place. Carefully lift the cover away from the unit and set it aside.
3. Disconnect the blower motor from the control board - Once you remove the access cover, you will observe the control board that receives signals from the thermostat and sends commands to the heating and blower components. The blower motor is connected to the control board via a wiring harness or several individual wires. Trace these wires back toward the motor, then pull them away from their connectors on the control board. If you think you will have doubts about where to reconnect the wires, take a snapshot with a digital camera before you pull off the connectors.
4. Unfasten the blower assembly from the furnace housing - After you have disconnected the blower motor wiring, locate the screws that hold the blower assembly in place. Depending on your model of furnace, it may be attached to rails or directly in the furnace housing. Remove these screws carefully while supporting the blower assembly to prevent it from falling. After all the screws are removed, slide the blower assembly out of the furnace and set it on the floor.
5. Remove the defective motor from the blower assembly - Once the blower assembly is on the floor, look inside the center of the fan, and you will see the motor shaft attached to the fan with a set screw. Loosen the set screw to free the shaft from the fan. Next, turn the blower assembly on its side so the motor is facing up. The motor is held in place on the blower housing with three or more braces. Remove the screws or bolts holding the braces to the assembly, then gently slide the motor up and out of the blower assembly.
6. Install a new motor - After the defective blower motor has been removed from the blower assembly, visit a heating parts supply store to find a new motor that will fit your unit. The store may grant you credit for a core replacement, so be sure to carry the part along with you.
Once you have the new motor in hand, insert it into the blower assembly and attach the motor braces by fastening the screws or bolts that hold it in place. Next, position the blower assembly on its end, so you can access the fan and set screw. Slowly turn the fan by hand until the flat side of the motor shaft aligns with the set screw on the fan. Tighten the set screw, so it presses into the flat side of the motor shaft.
7. Reinstall the blower assembly - Once the new fan has been installed in the blower assembly, carefully slide the assembly into the furnace housing and reattach it with the screws you removed in step 4. Next, push the connectors on the wires leading from the fan onto the control board; you may need to use a pair of needle-nose pliers to provide leverage when reconnecting the wires. Attach the access cover, then restore power to the furnace and check to see if the new motor is turning the blower fan as designed.
If this isn't a process that you feel comfortable doing on your own, reach out to a local company, such as United Heating Cooling and Plumbing Inc, for more information or to receive professional services.