If your car is having trouble with its blower motor resistor, it's good to know exactly what that part is, where it is, and why it might be giving you trouble. We'll walk you through exactly what the blower motor resistor is and some of the most common problems that drivers experience with this part. We’ll also detail what you can do about fixing it and what you can expect to pay to get the job done.
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What is a blower motor resistor?
Anytime you turn on the heat or the air conditioning in your car it works because a fan blows that air into the cabin where you are. It's one of the most easily taken for granted systems in your car because it seems relatively simple. After all, a fan is an uncomplicated piece of machinery as far as most of us are concerned. Push your button until some metal blades spin, and a breeze is created. It's not too hard to understand at all.
The same basic principle is what's behind how the air gets circulated in any vehicle. Behind those vents in your dashboard there is a blower motor that comes on when you need the heat or the air conditioning to work. Usually it's located in the dashboard on the opposite side of the steering wheel. You can't see it because it's inside the vehicle, but that's where it is located.
The blower motor resistor is the part of the blower motor that controls the speed. As you turn up the knob on your air conditioner, the resistor tells the blower motor to increase the speed and blow more air. Turn it down and the opposite happens. It's an electrical component and it works by sending electrical signals that correlate to the information you send by adjusting the dial. The electrical signal increases or decreases, and that affects the overall motor speed of the fan. As far as electrical systems go it's simple but as you can imagine if something interrupts that flow of electricity then you can potentially have a problem.
It's worth noting that when you turn the fan off completely, then there will be no power flowing to the blower motor resistor. And when you have the fan cranked up all the way in many vehicles, you will bypass the motor resistor all together because it's not needed to regulate the flow of electricity at that point. It's only at the stages in between being completely off and completely full blast that the blower motor resistor has a job to do.
Blower motor resistors are susceptible to a handful of problems that will affect their performance. For instance, moisture can get to a blower motor resistor and cause it to corrode. A corroded blower motor resistor can't regulate the current properly, and in turn will be unable to send the correct signals to the blower motor itself. That means potentially you will lose the ability to either increase or decrease the power of the fan. And in the worst-case scenarios it will send no signal at all and your fan will simply not work.
Aside from corrosion it could simply be mechanically damaged such as if you got into an accident and the resistor breaks in some way.
What are the symptoms of a bad blower motor resistor?
There are a handful of signs that the blower motor resistor has gone haywire in your car. Sometimes the symptoms overlap with issues in other systems in your car so you may need a professional to help you diagnose them. These are some of the most common things to look out for.
- No Air. As obvious as it may sound, one of the most prominent symptoms that you can be on the lookout for is a lack of air flowing through the vents when you're trying to get the heater or the air conditioner to work. When you turn the knob or press the button and it's supposed to start blowing air, if you feel nothing at all coming out that's a good sign that the blower motor resistor has failed on you. This can be a symptom of several other problems as well, so don't take it as a guarantee if this is the only symptom you're experiencing.
- High speeds only. As we mentioned earlier, a blower motor resistor isn't necessary in two instances. When the fan is off completely, or when the fan is running at high power. At high power the current bypasses the resistor because it doesn't need to be modulated it anyway. So, if you find that your heat and air conditioning can only go from being off completely to being on at high power it's almost guaranteed that the problem is you have a faulty blower motor resistor.
- Low speed only. It seems a little paradoxical to say that when your fan works at low speeds only it may be a symptom of a bad blower motor resistor given what we just said about how the high-speed only works as a symptom. Nonetheless, when there is a wiring issue between the blower motor resistor and the blower motor itself, it's possible that it can only work at low speeds.
- Fan won't turn off. If your fan doesn't turn off no matter what you do, and it's constantly running regardless of how you tried to turn it up, down or off, that means the blower motor resistor isn't regulating the electrical current properly.
- Blower motor works on some settings but not others. Your blower motor should have a range of settings that it works on from low up to high with several mid-range settings. If you're finding that some of those middle settings work and some of them do nothing at all it likely means there's an issue with the switch and how it sends the signal to the blower motor resistor about what it is you're trying to set the blower motor to.
- Smoking vents. This is an unlikely symptom of a bad blower motor resistor, but it's not impossible. If there is a short of some kind around the blower motor resistor and wires start melting the fan could blow the smoke from those melting wires back into the cabin of your car. A good rule of thumb is that if any smoke starts coming in through the vents of your car, you really need to pull over quickly and figure out what the problem is. If it's not the blower motor resistor, it's something even more serious and you really need to get that checked out as soon as possible.
- Burning smell. Very similar to the smoking vent issue, sometimes it's not as serious as actual smoke billowing into the cabin of the car but you will notice that distinctive burning smell that lets you know some metal or plastic is overheating somewhere in the vehicle. Often this will accompany one of the other symptoms that we've already listed.
Often a bad blower motor resistor can be diagnosed with a visual inspection. As we said, this part is located behind the dashboard on the passenger side of the car. In some models that could be reached through the glove box, but in others the dash would need to be removed entirely to get to it. For that reason, it is not always easy for someone to manage this task at home. Once you do get access to it though if you're lucky you'll be able to see right away if the part is corroded because if that is the problem it should be immediately apparent just by looking at it.
If corrosion is not the problem, then another way to test to see if the blower motor resistor is malfunctioning would be to attach an ohmmeter to it and measure the resistance. It should read at 4 to 5 ohms if it's working properly. If it gives another reading, such as an open circuit, it means that the resistor has failed and needs to be replaced.
It's possible that a blower motor resistor will fail because the blower motor itself has a problem. In cases like this even when you replace the blower motor resistor the blower motor itself may still be struggling and cause the resistor to fail again quickly despite being a new part. One way to diagnose this is, after replacing the blower motor resistor, turn on the fan and if there's a noticeable screeching, grinding, or whirring sound coming from the blower motor then you know that it may be the worn-out part. If that's the case, then the blower motor will have to be replaced as well. If it's not replaced, it may continue to stress the blower motor resistor and cause that to fail again as well.
How much does it cost to replace a bad blower motor resistor?
A blower motor resistor is not one of the more expensive parts to replace on a car. Head over to AutoZone right now and you'll find a wide selection of blower motor resistors that start as low as $12 and can range up to $50 or $60. As far as car parts go, that's not too bad overall.
The labor costs associated with repairing and replacing the blower motor resistor are obviously going to vary depending on what part of the world you live in as well as the make and model of the car you drive. If you drive an older vehicle, or something that is a little rarer, then you're going to have to expect that the repair costs are going to be higher than the average for you. If you've ever had to get something repaired and gotten estimates from shops around town, you've also noticed that one mechanic may charge nearly twice as much as another mechanic for the very same job. It really depends on the nature of the work, and who's doing it.
All things being equal, repairing and replacing a blower motor resistor is not nearly as complex as replacing a blown gasket head, for instance. You can expect to pay in the neighbourhood of $50 to $150 in labor fees plus the cost of materials to get this part fixed.
Can I fix my blower motor resistor myself?
Whether you can fix a blower motor resistor on your own clearly depends on how much you know about blower motor resistors and auto repair in general. If you're reading this guide about blower motor resistors and what they do, odds are you're not that familiar with them to begin with. For that reason, we would recommend against trying to fix this yourself because this is not beginner level repair. That's not to say it would be impossible for you to handle replacing the blower motor resistor yourself, but it would be a complex job.
Problems with the blower motor resistor are generally caused by failures in the car's electronic systems. If you're not completely familiar with your car's electronic systems and how they interact with one another, then it could be opening a whole new can of worms to try to get in there and fix this on your own. The result could be an even bigger problem when you're finished.
Naturally if you do want to take this job on yourself the best thing you could probably do is search out a YouTube video like this one that details in a step-by-step fashion how to fix the blower motor resistor. You can look up a guide that walks you through step-by-step, but it's much easier to do this kind of work when you can actually see the parts and see what the mechanic is reaching for, and how they're handling the replacement. Ideally you want to find a video walkthrough that deals with your exact make and model as well because the difference between a 1965 Aston Martin and a 2015 Nissan Altima are pretty much night and day.
The final word on this is that you can of course attempt to replace the blower motor resistor yourself, as the part is affordable, and the overall process doesn't require a ton of specialized parts. It's still an in-depth procedure that may test the limits of your automotive repair skills if you're not already comfortable working around under the hood of your car. Our recommendation is to leave this one to the professionals.
Final Thoughts
The blower motor resistor is a small and affordable part. Your car can of course function without it, but your level of comfort will suffer if you're not able to manage the heat and the air conditioning in your vehicle. If you're experiencing a problem with the air flow in your vehicle, you'll definitely want to get this problem diagnosed and fixed just for your own peace of mind and because you don't want it to lead to a bigger problem with your electrical system.