4 Symptoms Of A Bad Or Failing Blower Motor Resistor

Signs of a Bad Blower Motor Resistor

When you get in the car and expect a temperature-controlled ride, you don’t want to deal with any issues. Yet the symptoms of a bad blower motor resistor can cause a lot of problems that make your drive anything but comfortable. 

In this guide, we discuss the most common bad blower motor resistor symptoms and show you how to test it. We also talk about the function and location of the blower motor resistor before we reveal how much it may cost to replace it. Keep in mind that if the resistor is blown and the fan spins slowly or heavily, it may also need to be replaced, but we will discuss that more in a little bit. 


Symptoms Of A Bad Blower Motor Resistor

When the blower motor resistor goes bad, the motor can get stuck at one speed. The various airflow settings may also fail to work or you may not get any air from the vents. Furthermore, it can cause an inconsistent or intermittent fan speed, leaving you without proper airflow.

Dive into these symptoms with us. 

1. Blower Motor Only Works On One Speed

air condition controls

Most of today’s heater and air conditioning systems come with multiple fan speed settings. You should be able to easily choose the setting you want the fan on. Yet, one of the most common symptoms of a defective blower motor resistor is when the motor gets stuck on one setting. If you can’t get the motor off of a high or low setting, the resistor could be the problem.

The blower motor resistor is in charge of controlling the speed that the blower motor fan operates at. So, when it fails or shorts, the motor can become stuck. You may still be able to get the heat or air you want, but you won’t be able to adjust the speed. 

2. Various Airflow Settings Not Working

If you attempt to change the airflow settings and some don’t work, the blower motor resistor could be causing trouble. When the internal components fail or a short occurs, you are going to notice these malfunctions when attempting to change the settings. As an example, you may be able to use the lower fan speed settings but not the higher ones or vice versa. 

However, other problems can cause the same trouble, such as a defective blower motor switch. Therefore, a proper diagnosis is needed before you replace any parts. 

3. No Air Coming From Vents

warm air from vents

One of the worst possibilities is when the air stops blowing out of the vents. With a faulty blower motor resistor, this problem is possible at any time. Power gets supplied to the blower motor through the resistor, so any short or malfunction can cut off the power.

Without air pressure coming out of the vents, you are going to be uncomfortably hot or cold in extreme weather conditions. Yes, you can roll the windows down, but that’s not always convenient, especially if it’s raining outside. 

It’s important to note that this problem requires a professional diagnosis. It may be that the blower motor itself has gone out. You want to be sure you are replacing the right part so the problem doesn’t continue. 

4. Intermittent Or Inconsistent Fan Speed

We’ve already discussed how you may only be able to get one setting to work or a particular speed to work. Yet, there’s also the possibility that the system is going to malfunction sporadically.

Therefore, you may be getting high air pressure one minute and it cuts out a minute later. These sporadic issues indicate trouble with the blower motor resistor or some form of electrical malfunction. 

What’s The Function Of A Blower Motor Resistor?

blower motor resistor

The blower motor resistor is an electric part that blocks or resists the flow of current to the blower fan motor. Because of this resistor, the fan speed can be changed from low to high and everything in between.

The higher the resistance, the slower the fan goes, resulting in less airflow, either cold or hot. As the fan goes slower, there’s not as much air circulating in the car cabin. However, you can quickly change the fan speed by adjusting the settings, which alters the resistance and sends the signal to the blower motor.

If the car only had a blower motor, it wouldn’t be adjustable. You would be stuck using the air conditioning or heater at just one fan speed. 

It needs an electronic device that alters the speeds. Many newer cars have upgraded from the traditional blower motor resistor to an electronic control module instead. 

Where Is The Blower Motor Resistor Located?

car blower motor resistor

The blower motor resistor is an electrical part found between the ventilation blower or fan and the power source. Typically, it’s inside a duct close to the fan. With a manual system, the resistor is connected directly to the dashboard switch, which only changes when you make the adjustment. 

Automatic climate control systems now use a computer that reads the temperature and makes adjustments for you. Fan speeds are altered depending on what the selected temperature is. 

How Do You Test A Blower Motor Resistor?

If you’ve given the heating and air conditioning system a quick look and can’t find anything wrong, it’s time to focus on the blower motor resistor. Usually, the fan is going to fail at certain speeds, which tends to be a clear-cut symptom of a bad resistor, but it’s still important to perform a diagnosis before replacing parts. Unless you know what’s causing the failure, you don’t want to simply throw parts at the problem. You could end up spending money on parts that aren’t needed. 

As professional mechanics, we must remind you that it’s not safe to bypass the blower resistor. It can cause you to start a car fire.

Instead, follow these steps or any that are found in your service manual. 

  1. Examine the blower motor resistor visually. You are looking for signs of burning or corrosion. If you see either of these signs, you need to replace the resistor and damaged connectors. Yet, you must be sure to splice the wires correctly, or you will run into the same problems. 
  2. Check the resistance of the resistors with your multimeter. It must read ohms and you want to connect one probe to the common output terminal and the other to the input terminals. Reference your readings with the schematic in your service manual.
  3. If there’s any infinite resistance shown, the resistor needs to be replaced because there’s an open circuit. 
  4. It’s also possible that you need to replace the fan if it is spinning slowly or too heavily. 

Also, only handle the blower resistor with care. There are electrical currents passing through the auto part, so it can build up heat. The heat can get warm enough to burn your fingers. 

How Much Does It Cost To Replace A Blower Motor Resistor?

The average replacement cost of a blower motor resistor is between $90 and $175. Expect to spend about $40 to $100 on the part and another $50 to $75 for labor if you can’t perform the replacement yourself. 

However, you should bear in mind that the most common reason for a bad blower motor resistor is due to a bad fan motor. Therefore, in most cases you should replace both the motor and the resistor for a long-term repair.

If all you need is the resistor, you can expect this to be one of the cheapest automotive air conditioning repairs. However, it’s possible that other parts need to be replaced at the same time, increasing your total expenses. For example, if you need to install a new motor, the cost could go up another $500.

Your replacement costs depend heavily on the following factors:

  • Age/make/model of vehicle
  • Location of repair
  • Type of shop used (dealership vs. independent)

The good news is that it’s not difficult to replace the resistor. If you have some basic mechanical knowledge and generic mechanic tools, you can do it yourself. As professionals, we feel confident telling most drivers they can handle this replacement on their own. Give yourself an hour or two to complete the job if you have a service manual to follow. 

Can you drive with a bad blower motor resistor?

Yes, you shouldn’t have any issues driving with a bad blower motor resistor. The drive may be uncomfortable, depending on what the weather is like. The only time that a safety issue would be present is if you need to clean the windshield and the defrosters aren’t working. 

How long do blower resistors last?

It shouldn’t fail, as the part was designed to last for the lifetime of the vehicle. However, this part also endures a lot of stress, causing it to fail prematurely. If the heater and air conditioning are used continually or it’s exposed to excessive heat, it could fail on you.

Should I replace the blower motor if the resistor is bad?

Yes, in many cases is the blower motor causing the resistor to blow the internal fuse. However, if you are sure there’s nothing wrong with the blower motor and the resistor is going to fix the issue, you may not need to replace the blower motor.

What happens when a resistor burns out?

If the blower motor resistor is bad, your blower motor can get stuck on a single speed. There could also be various airflow settings that won’t work or you could fail to get air at all. On top of that, the fan speed can become inconsistent or intermittent, making for an uncomfortable drive. 

How long does it take to change a blower motor resistor?

It’s going to take a professional repair shop less than an hour to change the blower motor resistor in most cars. It’s not a complicated job. If you want to do it yourself, allot two hours just to be sure. Use a service manual or watch YouTube videos for installation directions based on your specific car model. 

The blower motor resistor isn’t a part that’s talked about until there’s an issue with the heating or air conditioning functions. As soon as the cabin becomes uncomfortable, you want to test the resistor to see if it’s causing malfunctions with the fan speeds. While it’s not a dangerous problem, no one wants to drive in hot or cold conditions.

You could probably change the blower motor resistor yourself, especially if you are accustomed to working on your vehicle. It’s not a difficult part to find or replace. Yet, it’s okay to reach out to a professional if you aren’t sure of yourself or you don’t have the time to invest. 

Categories: Air condition

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