If you hear a rattling noise in your car air vent, you’ll want to inspect the blower motor. We cover how to tell if the blower motor and blower motor resistor are causing problems with heating, ventilation, or air conditioning (HVAC) controls, like a musty smell, fan settings not working, or a rattling or loud noise from the vents in your vehicle.
What Is Causing a Rattling Noise in My Car Air Vent?
If you turn on the heater or AC controls and hear a rattling noise from the vents, it’s time to inspect the blower motor.
What Is the Blower Motor?
The blower motor circulates air throughout the HVAC system in your vehicle. The shape and size will vary depending on the car.
Where Is the Blower Motor Located?
Most blower motors will be located underneath the dash on the passenger side. They’re usually behind the glove box, but you might also find the blower motor in the engine compartment against the firewall.
How to Inspect a Blower Motor Causing a Rattling Noise or Working Intermittently
Steps to diagnose a rattling noise or smell in your car air vent
- Check the Fuse
In the video featured in this article at 1:35, we demonstrate an issue with the fan settings where there is no noise on low or high.
For a situation like this, you’ll want to check the fuse for the blower motor or HVAC system. Connect a test light and probe either side of the fuse to see if it’s working. Remove the fuse and check for a broken wire, which indicates it’s blown. A blown fuse will prevent power from moving to the rest of the circuit.
More on how to test fuses in your car
- Test the Blower Motor Resistor and Switch for Power
If the fuse is good, find a wiring diagram for this circuit. Generally, you’ll have power from the fuse to the switch.
If there is power at the switch, next you’ll want to test the blower motor resistor on all fan speeds. The resistor will have a different resistance per speed, and you want power on all speeds. If the resistor has power on all speeds and the fan still isn’t working, you’ll need to replace the blower motor.
The blower motor resistor is the most common reason for problems with the blower motor. The resistor decides how much power goes to the blower motor. The more power it has, the faster the motor will go. If the blower motor only works on certain speeds, then the blower motor resistor is defective and you’ll need to replace it.
If you’re replacing the blower motor resistor, we recommend replacing the blower motor at the same time.
- Inspect the Connector on Either Side of the Blower Motor Resistor and Blower Motor
Check the wiring harnesses on either side of the resistor and blower motor. If the blower motor has mechanical issues, it could overheat the wiring and cause an issue transferring power. If you find an issue with the resistor, blower motor, or the electrical connector between the two, we recommend replacing all three.
- Inspect the Blower Motor and the Electrical Connector
If you hear rattling in your car vent or other strange noises from the dash when using the HVAC controls, inspect the blower motor and it’s electrical connector for damage.
The blower motor may not be able to turn if an object like an acorn is caught in the splines. This can create excessive heat if the controls are on, and the inability to move will damage the motor or cause damage at the electrical connector. Check the electrical connector for melting, as seen in our video at 5:00.
The blower motor could make a rattling noise if it’s not mounted properly. It could be sitting off kilter and hitting another object. You might hear a squeaking noise when you turn on the heater or AC. This is caused by debris or rust in the windings, like from moisture accumulating on the bearings.
Remove the blower motor and check for any debris. If you find debris in the motor you can clean it out and it might work. If you remove the blower motor and find its components are loose or destabilize easily, the blower motor is defective and you’ll need to replace it.
Check parts of the blower motor for damage, like cracking or missing pieces. If the cage is broken, you could replace the cage separately, but if the motor has been in use for awhile, we recommend replacing the entire blower motor assembly.
- Inspect the Cabin Air Filter
An issue with the blower motor or cabin air filter can cause an odor from the vents whenever you use the HVAC controls. The cabin air filter should filter air and collect debris before the blower motor draws air. Attaching an air freshner to the vents might temporarily help with any smells, but it won’t fix this problem long term.
You’ll usually find the cabin air filter near the blower motor. It’s usually underneath the dash or behind glove box on the passenger side, but you might find it in the engine compartment or underneath the cowl panel at the bottom of the windshield.
If the cabin air filter is missing, the blower motor can collect debris and make a rattling noise from the vents. If the filter hasn’t been replaced on time, it can accumulate moisture, and, combined with debris, it could create mold or compost that can emit a scent.
Check the cabin air filter for dirt and debris. If there’s a lot of dirt on the fins, replace it.
Learn How to Fix More Than a Rattling Noise from the Air Vents in Your Car
Find out how to diagnose and fix many different problems with your vehicle. Our how-to videos have tips from experienced mechanics to help you inspect and replace different parts on your car.
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