The blower motor is the heart of your furnace — without it, there is no way that the heated air can be moved throughout your home.
Blower Motor Types
There are two main types of furnace blowers, the direct-drive motor and the belt drive motor. Direct drive motors connect directly to the blower fan, so there are fewer parts between the motor and the fan to break down. This is one of the more common blower motors, particularly in gas fuel furnaces.
Belt driven motors have a belt that connects the motor to the blower fan. The belt connects the fan via a pulley between the fan and the drive shaft of the motor. These are common on older furnaces but have been phased out in most newer furnaces.
Symptoms of Damage
A blower motor tends to either fail completely and rapidly or to slowly degrade. When the motor fails completely, you will have no heat coming from the vents and the fan will not come on. Typically the furnace will completely fail to operate.
A slow decline may first show as reduced heating or airflow from the vents. There may also be odd noises when the blower is operating. Squeals are particularly common, either right as the fan kicks on or even continuously throughout the entire cycle. You may also notice a bad odor, such as the smell of overheating oil, hot metal, or burning rubber.
Damage Causes and Repair Options
Poor lubrication is a common cause of a burnt-out motor. Without lubrication, friction will eventually damage the motor as well as the bearing in the fan assembly. Once the damage has occurred, the only option is to replace the part that suffered friction damage. If you are lucky, the repair will consist of repacking the bearings in the fan. If you aren't as lucky, the entire motor will need to be replaced.
Overheating is another common cause. Although overheating can be a side effect of poor lubrication, it can also happen for a variety of other reasons. For example, electrical issues and shorts may lead to overheating or a broken or imbalanced fan. Your tech will have to find the cause of overheating before they can determine whether repair or replacement is necessary.
For belt-driven motors, often the only necessary repair is to replace the worn belt with a new one.
Contact a furnace repair service if you suspect that the blower motor requires repair or replacement.