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.
Before you begin, it is important to shut off the power and close the gas valve to the furnace. Wait a few minutes for the system temperatures to cool down.
Remove the top cover panel first; it may have a simple twist-lock or push-lock, or you may need a screwdriver. With this top panel out of the way, you will have access to remove the blower cover panel.
Before you continue from here, you should put on gloves to safely remove the blower assembly.
Unscrewing the mounting screws on the tracks will allow the assembly to slide out, though you may need to first remove the control board if it is in front of the motor. If this is the case, you should take detailed notes or a picture of the wire configuration so that you can reconnect them correctly afterward.
After sliding the blower assembly out, check for a screw that secures the blower wheel to the motor shaft before flipping the assembly over.
Even if you think the problem is with the capacitor, you should always assume that it is charged and presents a risk of a serious electrical shock. To remove any potential charge from the capacitor for safety, place a screwdriver with an insulated handle across both terminals at the same time, making sure to not touch any metal on the screwdriver, before disconnecting the wires and removing it. When choosing a replacement capacitor, ensure that the capacitance (MFD) exactly equals that of the motor and that the Voltage rating (V) is equal to or higher than that of the motor.
Next, you can remove the mounting screws holding the motor to the housing with a socket wrench and remove the motor in its mounting bracket. Before removing it from the bracket, make sure to mark the position of the motor so that you will be able to align the new motor with the position of the old one.
You can use the model number (MOD) on the motor nameplate to search for an Original Equipment Manufacturer (OEM) motor, or you can just use the electrical specs listed on the plate to find an adequate replacement, keeping in mind that you will need to match the physical diameter, shaft size, and mounting type as well as the electrical requirements.
After reassembling the blower with the new motor and capacitor and/or new blower wheel, make sure that the cover panel for the blower is properly aligned, as there may be a switch that will cut power to the furnace if the cover is not replaced correctly.
Once you have replaced the top cover, reopened the gas valve, and turned the power to your furnace back on, you should find that it is running properly.
If you are unsure about any of the steps in this process, including selecting the right motor or determining the issue with your system, you should never hesitate to contact a professional here at Telco to ensure the safety and success of your project.