We’ll be discussing changing a right away drive blower motor and capacitor with a traditional up flow gas furnace as could be present in a basement of the home because these kinds of furnaces are probably the most common. Changing motors in horizontal units in an attic or a crawl space are very similar but will vary with the equipment. If you are not comfortable with working on 120-volt equipment please consult a professional Heating and Air Conditioning company to do this work.
Before we start, we go turn off the primary 120-volt capacity to the furnace. This can be capable of being accomplished by switching off the switch in the furnace in which the main power enters the furnace. Sometimes this switch is installed on a floor joists over the furnace, or along the side of the furnace itself. On the interest of safety, all of us shut the breaker off on the main house panel. We use a voltmeter to be sure the power is really off.
The next thing is to get rid of the screws or bolts that keep the blower assembly up within the furnace. Some blowers are on a sliding track while others are simply held in by these bolts or screws so it is a good idea to use a small 2″x4″ piece of lumber to lower the blower out of the furnace as the holding screws are removed. If there is a control board attached to the blower assembly all wires should be labeled so that if any wire is knocked off it can be reinstalled on the correct terminals that it came from. Hopefully, the blower assembly should come down with the wires in position. If there is a control board mounted on the blower we will have to remove it with the wires all attached and tie it up out of harm’s way. This is also true of the other component installed on the assembly.
Once all this is done we should be able to remove the wires from the motor and capacitor, but first, the capacitor wires must be shorted out with an insulated screwdriver by touching the screwdriver to both terminals on the capacitor together. Not this will lead to us finding a nasty shock when we touch those terminals with bare hands! Now we remove all of the motor wires in which they’re connected to the furnace control board or fan center (we’ve labeled each one of these wires before).
Once the blower assembly is on the floor, we turn it on its side and remove the screws or bolts that hold the mounting bracket to the assembly. You have to turn the blower once again and take off the set screw or bolt that supports the motor shaft to the wheel in the hub. With this done, we should be able to turn the assembly on its side and the motor should drop out of the assembly. We’re saying “should” because 7 out from Ten times it’ll, another Three times we’ll need to gently tap in the end from the shaft using a brass drift and hammer to push out of the wheel. Often we’ll need to use WD40 around the shaft first and often might need to use sand cloth around the shaft when there is any rust present. Beating in the shaft using a hammer will ruin the shaft and it’ll not emerge from the wheel! A brand new wheel is going to be needed when this happens.
Using the motor out we could now release the mounting bracket and fix it for the new motor. Some motors have the bracket welded to the motor from the manufacturer so they will not require this step. Now everything is reversed for the reinstallation of the motor. We should make sure the wheel spins freely on the assembly without hitting anywhere before we raise it back using the 2″x4″ lumber to the furnace. Once it is bolted back in place we reach into the wheel area and spin it once again to be sure it is running free.
All that is left is to reinstall the wires (including the green ground wire that goes to a metal unpainted part of the blower), on the control board or fan center and mount the new capacitor or reuse the old capacitor if it is the correct one for the new motor. We now go turn on any power source switches and or breakers that we previously had shut off. Turn the thermostat up to call for heating and our furnace should be running at this point. Make sure the rotation from the motor is really blowing air with the registers, or else we might need to turn back rotation wires in the motor. We’ll now look into the amp draw from the motor with the amp meter and compare it on the amp rating that’s in the motor or documentation that included the motor so that the motor is working as it must be. This amp draw check should be completed with the blower door on, however.
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