The blower motor relies on a capacitor to start and run smoothly. Set your multimeter to measure capacitance and connect the probes to the capacitor terminals. A reading that matches the capacitor's rated value indicates it is functioning correctly. If the reading is off, the capacitor may need to be replaced.
To test a blower motor with a multimeter, first set the multimeter to the "resistance" or "ohms" setting. Then, touch the probes of the multimeter to the terminals on the blower motor. If the resistance reading is infinite, that means there is an open circuit and the blower motor is defective.
You can test this by jumping out 120 volts to the blower motor wires; this will let you know if the blower motor works or not.
No Airflow
If you notice that there is no warm air at all coming through your heat registers, then you may have a broken blower motor. This generally means the blower motor has failed completely, which may indicate there have been problems for a while.
Typically, the lifespan of furnace blower motors spans from a minimum of 10 years up to about 20 years, with most enduring an average period between 15 and 20 years.
If the motor is making rattling, clanking, or banging sounds, it may be because of a loose or broken part inside the system. Loud banging sounds are especially worrisome. They're usually a sign that something within the system is damaged or disconnected, potentially indicating the need to replace the blower motor.
Make sure that the power cord hasn't melted or a fuse hasn't been blown. If your cables are looking fine, try unplugging the fan for a few minutes and then plugging it back in again. Sometimes, this process can reset the motor and solve your furnace problems.
On some platforms, a faulty blower motor relay will cause the blower not to work at all, which means there will be no airflow from the A/C. On others, the blower won't work on “high blow” but all the other speeds will work. The blower motor relay fails because it regularly deals with high current loads.
A sail switch would be used to prove that the combustion blower motor is operating before ignition. In this case, the sail switch will be used as a safety device. A sail switch is installed in the blower housing of an HVAC system's combustion blower assembly.
Use a multimeter or an ohmmeter to test the voltage of the electric motor. If there is no resistance or the resistance is uneven, the motor is likely faulty. Check the bearings to make sure they can spin freely. If they can't, lubricate them.
An HVAC blower motor will occasionally fail due to age, wearing out, or not being cleaned regularly. Symptoms may include strange noises, burning smells, or just plain refusing to turn on.
Replacing a furnace blower motor costs $560, on average. Depending on the size and type of motor, most people pay $300 to $900. The average blower motor replacement cost is $560, but the final price depends on labor fees, as well as the cost of the parts.
Strange Rattling, Clanking, or Screeching
One of the first signs you may notice when there's an issue with the blower motor is a strange noise coming from the indoor unit or air handler.
The blower motor relay is typically located in the HVAC system's electrical control panel or furnace control board. The exact location can vary depending on the specific system and its configuration. In some systems, it may be integrated into the control board, while in others, it may be a separate relay module.
In most newer systems, the button is often directly next to the blower motor, while in older systems, it may be harder to spot as it is sometimes underneath or behind the motor. The reset button is often made of yellow or red plastic and marked with a large “R ” to make it easier to spot.
Intermittent Operation
When this happens, there's usually something wrong with either the blower motor itself or with another part of your furnace that controls it. Problems include dirty filters, broken wires, poor voltage supply and faulty limit switch or capacitor.