Replacing a Blower Motor on a Furnace
If your furnace air is not circulating properly, it may be a sign that the blower motor needs to be repaired or replaced.
Do keep in mind that your blower fan does not immediately turn on along with the furnace; when the burner is lit, the heat exchanger must warm up before the blower fan will activate, as this prevents it from circulating cold air. However, if your furnace has had adequate time to heat up and the motor of the blower fan is still not turning, then it may not be receiving power, it may be seized and need to be repaired, or it may be burned out and need to be replaced.
Determine the Issue
First, listen to the furnace with the power on. If the blower is noisy or grinds when it spins, then it is likely the blower wheel has been damaged and needs to be replaced, rather than an electrical issue.
Next, determine if the motor is receiving power or not by letting the furnace try to run for about ten minutes. Then, after ensuring that the power to the furnace is off, carefully reach in toward the motor; if it has been receiving power and trying to start for the past few minutes, then it will be very warm. Be careful, as it may be very hot to the touch, to avoid burning your hand. If it is cold, you should investigate further for a potential power issue within the entire system.
If it is warm, reach around to the shaft/fan end, wearing a pair of gloves, and attempt to spin the motor by hand; if it resists with no obstruction to the fan wheel and does not spin freely in addition to being very warm, it is very likely that the motor has gone bad and needs to be replaced.
However, if your motor requires a capacitor to provide a magnetic phase shift to get the motor running, then it is also possible that it is actually the capacitor that has weakened or failed and needs to be replaced, so you may need to check into the capacitor with a meter as well.
Replacing a Blower Motor
If you are replacing the blower motor on your furnace, then in addition to the motor and/or capacitor, you will need a screwdriver, a socket wrench or nut driver, an adjustable wrench, and gloves to protect yourself from being cut by any sheet metal.