Although the soul of a home's forced-air HVAC system lies in the equipment that heats and cools the air, the heart of the system is the blower motor that circulates the conditioned air through the ductwork and out the various room registers. The blower motor is in many ways the hardest working component in the system since it is pushing air for both the heating and the cooling cycles. The same blower motor that does the job in the winter when the furnace is running is also blowing air in the summer when the air conditioner is operating. It's no surprise that this hardworking component may need attention sometimes.
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Blower Motor Basics
The appearance and location of the HVAC circulating fan and blower motor vary depending on the age and design of a furnace, but in most cases, it is a cylindrical rotating fan with an attached motor that sits in the bottom furnace compartment below the burner chamber. This fan design is generally known as a "squirrel cage" since it resembles the little exercise wheel used in cages that hold domestic squirrels, mice or other pets. This blower circulates air from the system's air return ductwork up through the heat exchanger or air conditioner evaporator coils and then through the air plenum and ductwork to the room registers.
In older furnaces, the motor that drives the squirrel cage blower is sometimes mounted on the side of the blower, and it spins the fan by means of a belt that transfers the spinning motion from the motor's spindle to the fan spindle. With this type, the motor and blower are separate units, and repairs and replacements can involve either the motor or the blower or both together.
Newer furnaces usually use direct-drive designs in which the motor's spindle directly drives the blower wheel. With these types, there is no fan belt to adjust or replace, and the motor and blower may be joined together as one integral unit. The motor portion may be inside the blower wheel or attached to the end. With this type, it is usually possible to remove and replace just the blower motor, but with some designs, these are integrated units that are removed and replaced as one piece.
Identifying Blower Motor Problems
Blower motor repairs can be as easy as tightening some bolts or vacuuming out dust or as complex as complete removal and replacement, and you won't always know what repair is needed until you examine the blower fan and motor. Often, this is a process of systematically inspecting and performing simple repairs until you've solved the problem. Sometimes, though, the nature of the symptoms will give you a hint as to what repairs are needed.
Blower Motor Symptoms and Likely Remedies
Fan makes rattling or banging noises
Mounting brackets or spindle setscrew needs tightening
Furnace cycles on and off rapidly
Dirty squirrel cage fan needs cleaning to prevent furnace from overheating
Motor itself is noisy
Motor needs lubrication; motor bearings are worn out, requiring replacement of motor
Air volume passing through ducts and out registers is reduced
Fan and blower motor need to be cleaned
Fan no longer operates at variable speeds
Dirty blower fan and motor need to be cleaned; blower motor needs to be reset
Blower motor doesn't run at all
Power needs to be restored to furnace; blower motor needs to be reset (after cleaning); motor is burned out and needs to be replaced
Preparing for Blower Motor Repair
Be aware that not all furnaces are well-suited to DIY servicing. With some complex, newer high-efficiency furnaces, it will be quite hard for homeowners to identify and service the parts, and they may require much different procedures than those used for more standard HVAC systems. The processes described here will work for typical low-efficiency and high-efficiency furnaces but always follow the manufacturer's recommended maintenance procedures for your particular furnace.
Remember that some symptoms that seem to be related to the blower fan and motor may actually indicate problems elsewhere. For example, a furnace that cycles on and off rapidly may have a problem with the combustion venting or the heat sensors or it may simply have an overly dirty and clogged air filter. In fact, an air filter replacement is a good first step for almost any furnace repair. If the furnace blower doesn't come on at all, it might actually be a problem with the combustion vent system's draft inducer fan, not the main air circulation blower. The draft inducer is a component found on newer standard and high-efficiency furnaces, and problems with it can cause a variety of symptoms.
In other words, remember that furnaces, especially modern ones, are complex pieces of equipment, and problems with air circulation may not lie with the blower or blower motor at all.
The tools and materials required for blower motor repair are pretty basic. If you have a basic set of nut drivers and screwdrivers, an adjustable wrench, a flashlight or task light, a stiff brush, a shop vac and some lightweight machine oil, you'll be set for most repairs. Depending on the type of furnace and the nature of the problem, you may need to buy other parts, such as a drive belt or even a new motor.
Furnace Blower Motor Repair and Maintenance Tasks
Accessing the Blower Motor
Any blower motor maintenance or repair starts with locating and inspecting these parts. In most furnaces, these components will be located behind the lower access panel on the furnace, near the floor. First, turn off the power to the furnace and remove the mounting nuts or screws to remove the access panel. Many furnaces are designed so that you first need to remove the upper panel, which covers the burner chamber and control panel, in order to next remove the lower access panel. Often, there is a safety switch that is engaged by the panel; this prevents the furnace from turning on while the panel is removed.
Cleaning the Fan and Motor
A great many air circulation problems are caused simply because the squirrel cage wheel and motor get caked with dust and dirt. Where feasible, it makes the most sense to physically detach these parts from the furnace frame in order to brush and vacuum them, but when this is not possible, do what you can to reach into the blower compartment and brush and vacuum away as much dust and grime as possible.
Removing the blower fan and motor is usually a fairly simple matter of detaching the motor's electrical wire leads that run to the furnace's control board and then removing the screws that hold the blower and motor to the mounting rails at the bottom of the furnace. The electrical wire connections will vary depending on the design of the furnace, but in many cases, they are simple spade connections at the furnace's control board, which is usually located in the burner compartment behind the upper access panel. Take note of how the wires are connected so you can replace them when reinstalling the blower and motor.
After thoroughly brushing and vacuuming both the fan blower and motor, reinsert them into the blower chamber and bolt them back to the frame. Reattach the wire leads and then close the furnace panels, turn on the furnace and test its operation. Surprisingly often, this simple cleaning routine is all that's required to solve blower problems.
Resetting the Blower Motor
Simple overheating of the motor, often caused by a buildup of dirt, may have caused the motor to shut down. After cleaning, you may need to reset the motor — usually, there will be a red button on the side or back of the blower motor, and resetting is just a simple matter of depressing the button. After resetting, make sure to restore power to the furnace before testing its operation.
Adjusting or Replacing the Drive Belts
Older furnaces may have a blower design in which the motor is bolted to the side of the blower, with a drive belt that transfers the motor spindle energy to the squirrel cage wheel. If this belt becomes worn or loose, it can cause the blower to squeal or even stop running entirely.
This belt will be quite obvious as you inspect the blower compartment, and you should see visual damage if it's present. Test the tension of the belt by pushing on it, and if it seems excessively loose (moving more than 1/2 inch when you depress it), it may need to be tightened or replaced following the manufacturer's directions.
Oiling the Motor and Blower Fan
On older furnaces, there may be oil ports on the blower motor, which may call for periodic oiling of the motor bearings during your routine maintenance schedule. This is a matter of removing the caps and topping off the reservoirs with a few drops of light machine oil. Make sure to follow the manufacturer's directions for oiling the motor and for the type of oil to use. Newer blower motors are usually entirely sealed, and their bearings never require oiling.
If the blower wheel itself has lubrication ports, also add oil to these to lubricate the blower wheel's bearings. Some newer blowers are designed so that it's impossible and unnecessary to lubricate the blower wheel.
Replacing an Old Motor
The most extreme repair will come if all other solutions fail to solve the problem. Be sure to rule out problems with the furnace before you turn to replacing the motor. Though it sounds difficult, blower motor replacement is well within the skill level of a moderately experienced DIYer, and it can save you a couple hundred dollars on the cost of having a service technician perform the replacement. However, remember that some furnace designs are not very friendly to DIY work and do your homework before tackling a blower motor replacement. You may be able to find online information or a video specific to your furnace model.
After verifying that the problem indeed lies with the blower motor, make sure to purchase a motor that is an exact replacement for the one you have. Blower motors can last for as long as 20 years if maintained properly, but replacement after five years is not uncommon if the furnace hasn't seen proper maintenance. If your furnace is older, there is a good chance that you'll face a motor replacement at some point.
Replacement begins with shutting off power to the furnace, removing the access panels and then locating the blower and blower motor. They may be separate units bolted together, or they may form a single unit, often with the motor bolted to the end so that it extends into the center of the squirrel cage wheel. In either case, you will usually unbolt the entire assembly metal frame rails in the bottom of the blower compartment in order to remove it.
Begin the removal by disconnecting the wire leads connecting the motor to the furnace's control panel. These connections are usually found on a control board in the upper compartment of the furnace. They may be screw terminal connections or more likely spade connections if the furnace is a newer model. Pay attention to the color-coding of the wires, as you'll need to attach the new motor in the same fashion.
With the wire connections free and the motor/blower unit unbolted from its frame, you can simply extract the assembly from the lower blower compartment. Next, loosen the setscrew that holds the motor shaft to the blower using an adjustable wrench. If there's a grounding wire present that links the motor to the furnace frame, detach this from the motor. Unthread any bolts or screws holding the motor to the blower unit and then detach it from the blower.
Now it's a fairly simple matter of reversing these steps with a new motor. Insert the shaft of the new motor into the blower wheel, make sure the motor is oriented properly and tighten down the shaft setscrew. Bolt the motor to the blower assembly and reattach the grounding wire if present.
Make sure the new motor's capacitor rating matches the existing run capacitor. If it differs, then you may need to install a different run capacitor that matches the new motor.
Insert the blower/motor assembly into the blower compartment onto the mounting frame and attach the nuts or screws that mount it on the frame rails. Thread the motor's wires into the upper compartment and attach them to the control board in the same fashion as the old blower motor. Replace the access panels, restore power to the furnace and test its operation.
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