Why Does My Car Blower Motor Turn On And Off Repeatedly?

Does your blower motor stop working and start working again after a while (especially if you drive over a hump)? We have researched the cause of this problem and found that you can easily diagnose and fix this yourself.

A bad brush is usually the culprit for a car blower motor turning on and off sporadically. A bad brush causes loose contact in the commutator. Either the brush is too dirty, so electric conduction is obstructed, or too worn to fit tightly in the commutator as it spins.

Carbon brushes in the commutator are used to conduct electricity. As the brushes wear down over time, they lose their ability to conduct electricity. This causes your blower to intermittently turn on and off. Read on to learn how to diagnose this problem and how to fix it yourself.

technician-service-center-install-maintenance-blower, Why Does My Car Blower Motor Turn On And Off Repeatedly?

How To Diagnose Intermittent Blower Motor

If you got your car brand new, then it's unusual for its blower motor to run into mechanical problems under normal use. This is because you can expect it to last indefinitely as long as your car is running. When your blower motor begins to struggle to provide consistent airflow and operates intermittently, then it's a sign that there is some dead spot in the connection.

A dead spot is a common issue when you have either a worn or dirty carbon brush. This can cause the sporadic operation of your blower motor.

It can be difficult to pinpoint a dead spot if you're not a mechanic. Fortunately, there's an easy way to detect this problem, and we'll show you in a couple of steps!

But before you can start, you'll be needing an oscilloscope.

What Is An Oscilloscope?

An oscilloscope is used to view and measure electrical signals. It's a diagnostic tool used to determine whether the signal is continuous or periodic and whether the frequency is consistent with a specific function. Electrical signals are often shown in waveforms in a digital oscilloscope. 

Using an oscilloscope is simple, as long as you can read and follow the instructions provided.

Check out this 2-in-1 digital oscilloscope on Amazon.

Steps For Diagnosing An Intermittent Blower Motor


1. Connect The Oscilloscope To The Blower Motor

Clamp the oscilloscope into the dangling wire that connects to the resistor. 

2. Turn The Key On

You'll be turning the blower on, so obviously, you need to turn the engine on!

3. Adjust The Time Basis Where You Want To Monitor Amperage Fluctuations

Adjustment setting depends on the kind of digital oscilloscope you're using. You can check your user's manual on how to adjust the settings. 

4. Check For Ripples

In the field of electronics, ripples or waves in amperage can indicate electrical interference. A good rule of thumb is that the bigger the ripple, the more likely the interference is happening.

So, if you notice a large ripple in the amperage of an oscilloscope, then there may be an electrical problem or dead spots in the area.

You can watch this video for the illustration:

What To Do When You Have An Intermittent Blower Motor?

You can resolve the problem with your car's blower motor blowing intermittently by looking into the condition of the motor itself. If one of the carbon brushes is getting worn out, then you have two options: you can replace it or replace the entire blower motor assembly itself.

Replacing your entire blower motor assembly can save you money in the long run. This also gives you peace of mind knowing that the rest of the components are brand new and should take a while before they get worn out. 

In addition, you will have a hard time looking for a carbon brush replacement since manufacturers may have discontinued this part. This is a good excuse, especially if they want to make you buy the whole blower motor assembly for more money! 

On the other hand, if, after checking the insides of your blower motor, you found that the carbon brush is just dirty, you can consider cleaning it with fine-grit sandpaper.

maintenance-blower-motor-car dirty

How To Replace Blower Motor

  1. Remove the plastic panel from the glovebox to expose your blower motor.
  2. You should see some bolts that are holding the blower motor in place. Loosen them, and you should be able to remove the blower motor with ease.
  3. Slide the replacement blower motor assembly in and tighten the bolts.
  4. Put the plastic panel in and you're all set!

Watch the entire process below:

How To Clean Blower Motor And Replace Carbon Brush On A Car's Blower Motor

  1. Follow steps 1 and 2 on how to replace the blower motor.
  2. Loosen the nut that secures the blower motor fan and remove the fan.
  3. Unscrew the blower motor housing. You should see the motor exposed.
  4. Pull the motor out gently and locate the commutator. The commutator is a series of small rectangular metal pieces located on the motor shaft. You can't go wrong in locating it as it is the part that you hold on to next to the motor shaft.
  5. Spray contact cleaner onto the commutator.
  6. Apply a fine-grit sandpaper on the commutator until clean. You might as well clean the other parts while you're at it!
  7. Look for the carbon brush support rack which is most likely stuck in the blower motor housing. 
  8. Examine how the parts fit together. You should see two slots for the springs. Slide the springs in followed by the carbon brushes. These slots should serve as your guide on the proper placement of carbon brushes.
  9. Put the housing back in and follow the steps in reverse order to put everything back again. Don't forget to lube!

Check out this multi-purpose oiler on Amazon.

The entire process can be viewed here:

What Will Happen To My Car Blower Motor If One Of Its Resistors Goes Out?

A resistor is an electrical component that regulates current flow. Resistors come in various sizes, depending on the type of current they regulate. Each speed setting of your car's blower motor uses a different resistor.

For example, if the resistor that regulates current flow to the speed setting 1 of your blower motor goes out, it could cause that speed setting of your blower motor to not work. 

What Causes Blower Motor Resistors To Go Bad?


There are two main reasons why blower resistors go bad: corrosion and overheating.

The reason why corrosion causes a resistor to fail is that the resistor has a connection point that corrodes over time. If left unaddressed, the resistor can eventually fail and result in one of your blower motor speed settings failing as well.

On the other hand, overheating is the other main cause of the failure of blower motor resistors. The motor operates most efficiently when the temperature is set at the correct level as predetermined by your car's manufacturer.

When the temperature rises above the correct setting, the heat generated by the motor increases, which causes the motor to overheat. The worst-case scenario here is a fried resistor.

Is It Safe To Run A Car Without Blower Motor?

Most cars today come equipped with a blower motor to provide adequate ventilation inside the vehicle. The blower motor has nothing to do, not in any way, with the engine's cooling system as it has the radiator to do that job. 

How Much Cost To Replace Blower Motor?

Many people are unaware of the fact that a car's blower motor replacement costs are considerably less than its repair.

If you've decided to get it replaced, you need to know that the price may differ depending on the type of vehicle that you own and the moral values of the mechanic who will do the replacement.

On average, you can expect to pay between $50 to $100 for a new blower motor assembly and an additional $100 in labor costs. 


Replacing Blower Motor In A Car: How Long Will It Take?

If you haven't performed a blower motor replacement before, then you're probably thinking about how difficult it will be to replace a blower motor in your vehicle, and that's understandable. 

Well, it turns out that replacing a blower motor is a relatively easy process. It will require you to take the motor apart and replace a few parts before you're ready to reassemble it.

If you follow the steps above and if it's your first time, it will take you a minimum of six hours to complete the job.

How Long Does A Blower Motor In A Car Last?

A blower motor can last a lifetime of your vehicle if it's done right. However, you might have come across many people (or maybe you're one of them!) who's had their car repaired and has a broken blower motor.

But, why is that so? Is it possible for a blower motor to break in just a few years? It could be that they're the second owner of the car. Nonetheless. it's important to note that the blower motor will last longer only under normal use and if it is regularly checked and maintained.

In Closing


You have three options when your blower motor turns on and off intermittently: clean the carbon brush inside the blower motor, replace the carbon brush if worn out, or replace the entire blower motor assembly.

We have covered the procedural steps for each of these three options. Now it's up to you to determine which option is most appropriate for your situation.

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