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5 Frequently Asked Questions about Blower Motor Resistor

This article is a collection of 5 frequently asked questions about blower motor resistor.


I. What is a Blower Motor Resistor?

II. How Does the Blower Motor Resistor Work?

III. How Do I Know If My Blower Motor Resistor is Bad or Broke?

IV. How to Test a Blower Motor Resistor?

V. Can I Fix the Blower Motor Resistor by Myself?


I. What is a Blower Motor Resistor?

The blower motor resistor is the blower motor component that regulates the speed. When you raise the thermostat on the air conditioner, the resistor sends a signal to the blower motor to speed up and blow more air. When you turn it down, the opposite happens. It is an electronic component that sends electronic pulses corresponding to the information you send through the adjustment dial. The electrical signal increases or decreases, which affects the overall motor speed of the fan. As far as electrical systems are concerned, they are simple, but as you might see, if something interrupts the flow of power, problems can occur.


Behind these vents in the dashboard, there is a blower motor that starts when you need heating or air conditioning. Usually, it is located in the dashboard on the other side of the steering wheel. You can't see it because it is inside the vehicle, but there it is.


A digital speed controller controls a variable speed motor. The controller typically receives a digital input from the speed switch or HVAC control head. The control head then sends a command to the motor controller to adjust the speed to the driver's requirements.


The motor controller rapidly pulses the ground circuit on and off to achieve the desired speed. So a half-speed driver request will result in the blower motor controller pulsing the ground connection off twice as often as when the fan is running at full speed.


The blower motor resistor or control module is often positioned within one of the ducts in the HVAC system, close to the blower motor, in most modern vehicles. This is done so that the resistor or control module can be cooled by passing air. A blower motor resistor was fitted on the firewall of some older vehicles, with access from under the hood.

 II. How Does the Blower Motor Resistor Work?

This video will give a detailed explanation of blower motor circuit to help you better understand how eactly it works.

III. How Do I Know If My Blower Motor Resistor is Bad or Broke?

There are a few indications that your car's blower motor resistor has failed. Because the symptoms may overlap with difficulties in other systems in your vehicle, you may require the assistance of a specialist to help you diagnose them. These are some of the most typical warning signs.

(1)  No air. As simple as it may sound, one of the most noticeable indicators to look for is a lack of air moving through the vents when trying to get the heater or air conditioner to function. If nothing comes out when you turn the knob or press the button and it's intended to start blowing air, it's a good clue that the blower motor resistor has failed. This can be a sign of a variety of different issues, so don't take it as a given if this is the only signal you're receiving.


(2)  High speeds only. As previously stated, a blower motor resistor is not required in two situations. When the fan is totally turned off or when it is running at high power. Because the current does not need to be modulated at high power, it bypasses the resistance. So, if you discover that your heat and air conditioning can only switch from being completely off to being on at high power, it's almost certain that you have a broken blower motor resistor.


(3)  Low speeds only. When your fan only works at low speed, this may be a signal of poor blower motor resistance as well. However, when there is a wiring problem between the blower motor resistor and the blower motor itself, it may only work at low speeds.


(4)  The fan will not turn off. If you can't turn off the fan no matter what you do, and no matter how you try to go up, down, or turn off the fan, the fan is constantly running, which means that the blower motor resistor cannot properly regulate the current.


(5)  The blower motor works under certain settings, but does not work under other settings. The blower motor should have a series of settings, from low to high, which can be set in a variety of intermediate ranges. If you find that some of these intermediate settings are working and some of them do nothing at all, it probably means that there is a problem with the switch, and how the switch sends a signal about your settings to the blower motor resistor blower motor.


(6)  Smoking vents. This is an unusual signal of a faulty blower motor resistor, though it is not unheard of. If there is a short around the blower motor resistor and wires begin to melt, the fan may spew smoke from those melting wires back into your car's cabin.


A solid rule of thumb is that if smoke starts flowing in via your car's vents, you should pull over immediately and figure out what's wrong. If it isn't the blower motor resistor, it could be something more serious, and you should get it checked out as soon as possible.


(7)  Burning Smell. Similarly to the smoking vent issue, it is not always as dangerous as actual smoke billowing into the car's cabin, but you will detect the distinct burning smell that indicates that some metal or plastic is overheated somewhere in the vehicle. This is frequently associated with one of the other signals we've already mentioned above.

IV. How to Test a Blower Motor Resistor?

Blower motor resistor test

V. Can I Fix the Blower Motor Resistor by Myself?

Whether you can repair the blower motor resistor yourself obviously depends on how much you know about blower motor resistors and general car maintenance. If you are reading a guide on blower motor resistance and its functions, you may not be familiar with them. Therefore, we recommend that you do not try to fix this problem yourself, as this is not a beginner-level fix.


This is not to say that you cannot replace the blower motor resistance yourself, but it will be a complicated task. But we provide you with some basic methods to diagnose and repair some simple blower motor problems, for reference only. For specific steps, please consult professionals or check related videos on youtube.


(1) The blower only works in high speed.

This is a sure sign of a bad blower motor resistor, not a faulty speed switch. Change the resistor.


(2) The blower only works in low speed.

Check for a blown fuse or a faulty high-speed relay. Replace the high-speed relay with a relay of the same part number.

Check the fuse for the high speed relay's control side as well. Verify that the high speed relay's ground side is good.


(3) Repeated failures of the blower motor resistor

Check for full airflow at the vents. If airflow appears to be restricted or lower than typical, a blocked cabin air filter is to blame. Examine the cabin air filter. If everything is ok, look for debris on the evaporator or heater.

When the airflow is reduced, the blower motor resistor overheats and fails. Reduced airflow forces the blower motor to work harder and draw more current, which might result in repeated blower motor resistor failures.


1. What does a resistor do on a blower motor?

Blower resistors are resistors which are used to control the fan speed of automotive blowers. The fan speed can be changed either by switching the blower resistor resistance mechanically, using a rotating lever, or electronically by the air conditioning system.

2. Can I bypass blower resistor?

Blower resistors are resistors which are used to control the fan speed of automotive blowers. The fan speed can be changed either by switching the blower resistor resistance mechanically, using a rotating lever, or electronically by the air conditioning system.

3. What can cause a blower motor to stop working?

In a situation where the motor doesn't work on any speed, the most likely causes are: a blown power supply fuse, a bad motor ground connection, bad motor speed control module or a failed motor. On all systems, a failed blower motor is least likely. ... Start by checking the blower fuse and HVAC controller fuse.

4. How do you test a blower motor resistor with a multimeter?

Place one lead of the Ohmmeter on terminal 1 of the resistor. Place the other lead on terminal 2 and check against specifications. If this circuit is open, showing infinity on the Ohmmeter, the blower resistor must be replaced. Move the lead from terminal 2 to terminal 3 and check this reading against specifications.

5. Is the blower motor resistor supposed to get hot?

Yes that resistor will get very hot. Most people don`t know this but it is faster to defrost the windshield on low or medium fan speed due to that resistor putting off heat. Also that resistor needs to be cooled off with the air flow or it will burn up .

6. What is the function of a blower motor resistor?

A blower motor resistor is an adjustable resistor. This electrical component is used to control the air conditioning system of a vehicle. It is the part that controls the fan speed of the fan motor according to settings that can be changed by turning the knob to the left or right, thereby increasing or decreasing the resistance of the electric current flowing to the rotating fan motor connected to the fan.

7. Where is the blower motor resister?

A blower motor resistor, typically located beneath the passenger side dashboard, contains three resistors, or sets of terminals designed to generate voltage in proportion to electrical current.

8. How do you replace a blower motor resistor?

Safety Tip: Always wear safety glasses when working on your motor. Wear other personal protective equipment (PPE) when necessary, for example latex gloves or closed toe shoes.

1.Remove the negative battery terminal.
2.Locate the blower motor resistor on the passenger side under the dash board. It is mounted to the the blower housing near the blower motor.
3.Disconnect the electrical connector to the blower motor resistor.
4.Remove the screws or bolts to the blower motor resistor and remove the resistor.
5.Installation is the reverse of the removal.

9. Can you test a blower motor resistor?

Yes. Set your multimeter to Diod or continuity and place leads on either side of the resistor. If no tone and infinite resistance it is bad. If tone but no resistance it is bad. If you have continuity to ground, something has shorted to ground look for heat damage. If you have tone and resistance it is good. 

10. Why does a blower motor resistor keep going out?

If you are constantly blowing that part. You ether have the motor pulling to much amps. If it is home unit it could also be a inline control board cap.