Stuck in a hot car or chilly ride because your air vents aren’t doing their job? You might have a faulty blower motor (fan) resistor on your hands. This small but important component is key in controlling the airflow inside your vehicle.
The blower motor resistor adjusts the amount of power delivered to the blower motor based on the fan speed setting you select. Want a light breeze or a strong blast? The resistor regulates the electrical flow.
The resistor is generally easy to reach and located near the blower motor itself, under the dashboard inside the HVAC housing. When it starts to fail, you may notice the fan only works at certain speeds, not at all, or becomes unpredictable.
Knowing how it works and where it’s located can help you quickly spot problems and fix them yourself, keeping your drives pleasant and stress-free.
In this guide, we’ll help you identify the warning signs, diagnose the problem, and even walk you through replacing the resistor if needed. Let’s get started so you can get back to driving comfortably.
Signs of a Bad Blower Motor Resistor
The blower motor resistor is the usual culprit when your vehicle’s air system starts acting up.
Here are the common signs to watch out for:
- Inconsistent Fan Speeds: If the fan only works on certain settings and ignores others, this can be a dead giveaway. Often, you might only get airflow on the highest setting because that bypasses the resistor entirely.
- Intermittent Operation: The fan might cut in and out randomly, leading to frustration, especially on those extreme weather days. This can happen if the resistor’s connections are deteriorating or overheating.
- Weak or Reduced Airflow: Even with a functioning blower motor set to high, if the airflow seems weaker than it should be, the resistor could be partially at fault, limiting power to the motor.
- Fan Not Responding to Controls: If you twist or push the fan speed control and notice no change in airflow intensity, your resistor may be on the fritz.
- No Airflow at All: When the fan doesn’t work on any setting, it may indicate the resistor has completely failed.
Next, let’s look into diagnosing the little guy.
Diagnosing a Faulty Blower Motor Resistor
Diagnosing HVAC issues in vehicles with climate control requires an understanding of how these systems operate. Unlike basic systems, where controls directly adjust the fan, climate-controlled systems use a computer to manage the fan speed based on your inputs.
In these systems, pressing the controls sends commands to a central HVAC control module. It decides the best fan speed and temperature settings for maintaining your desired comfort level. This can sometimes make the system seem unresponsive if left in ‘Auto’ mode, as the computer manages settings for optimal efficiency. Always try turning the system off ‘Auto’ to assess if manual settings prompt any changes.
When diagnosing problems, remember that climate-controlled systems have several potential points of failure, including the control panel, blower motor (fan), resistor, or even the HVAC control module itself.
Here’s a step-by-step approach to narrow down the issue:
- Toggle Through Fan Settings: Check every fan speed setting by taking the system off ‘Auto’ mode. If the fan operates only on the highest setting, this often suggests a blower motor resistor is the issue.
- Inspect Fuses and Relays: If there is no blower at all – check the HVAC system’s fuses and relays, if fuses are good but no fan suggests a possible bad blower motor.
- Blower Motor and Obstruction Check: Verify that the blower motor is functioning and inspect for obstructions like leaves or debris that could influence airflow and create resistance. Check for power at the blower motor, power but no action means the fan motor is toast. No power at the motor points back to the resistor, wiring or control panel issue.
- Examine the Resistor: Locate the blower motor resistor, in the HVAC casing, and visually inspect it for burns or damage to connectors or corrosion.
- Test with a Multimeter: Remove the resistor and use a multimeter to check the resistor’s resistance. Refer to your vehicle’s service manual for the correct readings—mismatch indicates the resistor is shot.
In vehicles with climate control, problems may stem from the HVAC control panel or the control module. These components should be inspected further if basic troubleshooting doesn’t fix the issue. A scan tool is often required to activate the HVAC system and confirm proper operation. Additionally, climate control systems generate fault codes that can provide valuable diagnostic insights.
How to Replace Your Blower Motor Resistor
Replacing a faulty blower motor resistor is straightforward. Steps as follows:
Tools You’ll Need:
- Socket set (usually 7mm, 8mm, or 10mm)
- Screwdrivers (Phillips and flathead)
- Ratchet and extension
- Flashlight
Step 1: Locate the Blower Motor Resistor
The blower motor resistor is located under the dashboard on the passenger side, near the blower motor. In some vehicles, you may need to remove the glove box or a plastic kick panel for access.
Step 3: Remove the Old Resistor
- Locate the resistor, which is typically secured by two screws or bolts.
- Unplug the electrical connector by pressing the release tab and gently pulling it out.
- Use a socket wrench to remove the screws/bolts holding the resistor in place.
- Pull the resistor out.
Step 4: Install the New Resistor
- Position the new resistor in place, ensuring it lines up with the mounting holes.
- Secure it using the original screws or bolts.
- Reconnect the electrical plug, making sure it clicks into place.
Step 5: Test the New Resistor
- Turn on the vehicle’s blower motor and cycle through all fan speeds to confirm proper operation.
- If all speeds work correctly, the installation is successful.
You nailed it!
FAQs
Can I drive with a bad blower motor resistor?
Yes, you can still drive your vehicle with a faulty blower motor resistor, but your HVAC system may not function correctly. You might be stuck with no airflow, maximum speed only, or an inconsistent fan operation, which can make driving uncomfortable in extreme temperatures.
What causes a blower motor resistor to fail?
The most common causes of failure include overheating, corrosion, moisture exposure, and excessive electrical load due to a failing blower motor or restriction (debris). A blower motor that draws too much current can burn out the resistor over time.
How long does it take to replace a blower motor resistor?
Most replacements take 15 to 30 minutes, depending on accessibility. In many vehicles, the resistor is easy to reach under the dashboard, but some models require removing the glove box or trim panels, which can add to the time.
How much does it cost to replace a blower motor resistor?
A replacement blower motor resistor typically costs between $20 and $80, depending on the vehicle make and model. If you hire a mechanic, labor costs can range from $50 to $150, bringing the total repair cost to $70 to $230 on average.
Do I need to replace the blower motor when replacing the resistor?
Not necessarily, but if the blower motor is faulty or drawing too much power, it could cause the new resistor to fail prematurely. If your blower motor is noisy, weak, or intermittently failing, it’s best to test or replace it along with the resistor to avoid further issues.
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.