How to Change a Blower Motor Resistor: The Complete DIY Guide

Is your car’s fan stuck on one speed or not working at all? You might have a bad blower motor resistor. This little component controls your car’s fan speeds, and when it fails, your comfort goes right out the window. The good news? Replacing it yourself is totally doable, even if you’re not a car expert—and you’ll save a bunch of money.

What Is a Blower Motor Resistor?

A blower motor resistor is the electrical component that controls your car’s fan speeds. It works by creating different levels of electrical resistance to control how much power reaches the blower motor.

When you select a lower fan setting, the resistor blocks more electricity, making the motor spin slower. On the highest setting, your car typically bypasses the resistor completely, allowing maximum power to flow to the motor.

These parts handle significant electrical loads and generate considerable heat during operation. Manufacturers place them in the airflow path of the blower motor to keep them cool. Despite this design, they’re still prone to failure due to:

• Constant heating and cooling cycles
• Electrical stress from regular use
• Corrosion or moisture damage
• Debris buildup restricting airflow

Signs Your Blower Motor Resistor Is Bad

Fan Only Works on High Speed

The most common symptom is when your fan only works on the highest setting. This happens because the resistor has failed, but the “high” setting bypasses the resistor entirely.

Inconsistent Fan Speeds

Notice certain speed settings don’t work at all? Or maybe the fan jumps between speeds on its own? Your resistor likely has damaged internal circuits.

No Airflow From Vents

When you turn the fan control and nothing happens at any setting, the resistor may have failed completely, cutting off all power to the blower motor.

You Smell Something Burning

A burnt plastic or electrical smell often indicates an overheated resistor. This typically happens right before complete failure.

Strange Noises

Unusual rattling or buzzing sounds from your dashboard can signal resistor problems affecting how the motor performs.

Visual Damage

If you’ve already located the resistor, melted plastic, scorch marks, or damaged connectors are clear signs it needs replacement.

Tools You’ll Need for the Job

Safety First: Before You Start

1. Disconnect the battery: Always disconnect the negative battery terminal before starting. This prevents electrical shock and protects your car’s electronics.
2. Let everything cool down: If you’ve recently used your car’s heating or AC, wait at least 5 minutes for the system to cool. Resistors get extremely hot during operation.
3. Work in a well-ventilated area: You’ll be working in confined spaces under the dashboard, so good air circulation helps.
4. Use proper lighting: A good work light or flashlight is essential since you’ll be working in dark areas.

Where Is the Blower Motor Resistor Located?

Finding the resistor is often the trickiest part of this job. Common locations include:

Under the Dashboard

Most vehicles place the resistor on the passenger side under the dashboard, usually near or attached to the blower motor housing. You’ll typically need to remove the glove box for access.

On the Firewall

Some vehicles mount the resistor directly on the firewall in the engine compartment, usually on the passenger side near the heater hoses.

In the HVAC Ductwork

Modern vehicles often integrate the resistor into the HVAC ducts where it receives airflow for cooling.

How to Access the Blower Motor Resistor

If It’s Under the Dashboard:

1. Push the passenger seat back as far as possible to create workspace
2. Open the glove box
3. Look for plastic tabs or stops on each side of the glove box
4. Press these tabs inward while lowering the glove box beyond its normal open position
5. Some vehicles require completely removing the glove box by unscrewing mounting hardware

If It’s Behind Panels:

1. Identify which panels need removal (typically lower dash panels or kick panels)
2. Look for visible screws holding these panels
3. Use a plastic trim removal tool to carefully pry off panels that use clip attachments
4. Work slowly to avoid breaking plastic clips

If It’s in the Engine Compartment:

1. Open the hood and secure it properly
2. Look on the passenger side of the firewall (the wall between the engine and passenger compartment)
3. The resistor is typically a small rectangular component with a wiring harness connected to it

Diagnosing Before Replacement

Before installing a new part, confirm the resistor is actually bad:

Visual Inspection

Look for:

• Burn marks or discoloration on the housing
• Melted or scorched connector plugs
• Corrosion or rust on terminals
• Cracks or physical damage

Using a Multimeter (Optional)

If you have a multimeter, you can test the resistor:

1. Set your multimeter to measure ohms (Ω)
2. Test resistance between terminals
3. A good resistor shows specific resistance values (typically 1-8 ohms)
4. Infinite resistance readings indicate a broken connection
5. Zero resistance may indicate a short circuit

Step-by-Step Replacement Process

1. Preparation

1. Make sure the engine is off and cool
2. Disconnect the negative battery terminal
3. Remove necessary panels for access
4. Position your work light for best visibility
5. Have your replacement part ready

2. Removing the Old Resistor

1. Locate the resistor assembly (a small rectangular or round component with a wire connector)
2. Disconnect the electrical connector by pressing the locking tab and pulling straight off
3. Remove the mounting screws (typically 2-3 screws holding it to the housing)
4. Carefully extract the old resistor, noting its orientation for proper installation of the replacement

3. Installing the New Resistor

1. Position the new resistor in the same orientation as the old one
2. Install mounting screws (tighten snugly but don’t over-tighten as this can crack the housing)
3. Connect the wire harness, pushing firmly until you hear the locking tab click
4. Verify the connection is secure by gently tugging on the connector

4. Checking the Connector

The connector often gets damaged when a resistor fails. If yours shows melting or damage:

1. Cut the damaged connector from the wire harness
2. Strip wire ends carefully
3. Install a new connector following wire color coding
4. Apply dielectric grease to protect against corrosion
5. Secure connections with proper crimp connectors

Testing Your Work

Immediate Testing

1. Reconnect the negative battery terminal
2. Start the engine
3. Test each fan speed setting one by one
4. Listen for unusual noises
5. Check airflow volume at each setting

Complete System Check

Run both heating and air conditioning through complete cycles to ensure the resistor works properly under all conditions.

Troubleshooting Common Issues

If the New Resistor Fails Quickly

This often indicates deeper problems:

Blower Motor Problems: An aging blower motor with worn bearings can draw excessive current, overheating and destroying resistors. A healthy motor typically draws 15-20 amps maximum on high speed.

Airflow Restrictions: A clogged cabin air filter or blocked air intake reduces cooling airflow across the resistor, causing overheating.

Electrical Issues: Voltage spikes, poor ground connections, or faulty control switches can cause premature resistor failure.

Installation Problems

Loose Mounting: Ensure the resistor is properly seated and secured. Loose mounting causes vibration damage and poor heat dissipation.

Incorrect Wiring: Double-check wire connections against your vehicle’s wiring diagram.

DIY vs. Professional Replacement: Cost Comparison

Parts Selection

OEM vs. Aftermarket: Original equipment manufacturer (OEM) parts typically cost $75-$100 but offer guaranteed fit and reliability. Quality aftermarket parts range from $40-$70 and can provide excellent value.

Complete Kits: Some manufacturers offer complete replacement kits including the resistor and new connector pigtail for $50-$80, which is often the best value when the connector needs replacement too.

Preventive Maintenance Tips

Regular Inspection

Include blower motor resistor inspection in your annual HVAC maintenance routine. Look for early signs of connector corrosion or heat damage.

Keep Things Clean

Replace cabin air filters regularly to ensure adequate airflow across the resistor for cooling.

Change Speeds Gradually

Avoid rapid switching between fan speeds, which creates electrical stress on the resistor.

Control Moisture

Address any interior moisture issues that could contribute to resistor corrosion.

Specific Vehicle Considerations

Domestic Vehicles

Ford/Mercury/Lincoln: These often have the resistor mounted near the passenger footwell behind the glove box. Ford models typically use a 7mm socket for mounting screws.

GM Vehicles: Many General Motors vehicles place the resistor on the HVAC housing behind the glove box. Access often requires dropping or removing the entire glove box assembly.

Chrysler/Dodge/Jeep: These commonly locate the resistor on the firewall in the engine compartment, which simplifies access but makes it vulnerable to engine heat.

Import Vehicles

Toyota/Lexus: These typically place the resistor under the passenger side dash, often requiring partial disassembly of interior trim panels.

Honda/Acura: Many Honda vehicles locate the resistor behind the glove box, with access through a small panel that doesn’t require full glove box removal.

Subaru: These often mount the resistor in a more accessible location behind the glove box or under a dashboard panel.

Advanced Diagnostics

Testing the Entire System

If replacing the resistor doesn’t solve your problem, you may need to check:

1. Blower motor function: The motor itself may be failing
2. Control switch integrity: The switch that controls fan speeds could be bad
3. Fuse condition: A blown fuse can prevent operation
4. Wiring harness: Look for damaged wires or loose connections
5. Climate control module: In systems with electronic climate control, the control module might be at fault

Using a Circuit Diagram

For complex issues, consult your vehicle’s wiring diagram to trace the complete circuit from power source through the switch, resistor, and to the blower motor.

Why Blower Motor Resistors Fail

Understanding why these parts fail can help prevent future problems:

1. Heat damage: The constant heating and cooling cycles cause thermal stress
2. Vibration fatigue: Engine and road vibrations wear connections over time
3. Corrosion: Moisture in the HVAC system can cause terminal corrosion
4. Electrical overload: When the blower motor ages, it can draw excess current
5. Manufacturing defects: Some vehicles have design flaws that lead to premature failure

Final Tips for Success

1. Compare parts before installation: Make sure your new resistor matches the old one
2. Take photos before disassembly: This helps with reassembly
3. Label connectors: If multiple connectors are present, mark which goes where
4. Check for TSBs: Some vehicles have technical service bulletins about resistor issues
5. Buy quality parts: Cheap resistors often fail quickly
6. Clean the area: Remove any debris around the resistor mounting area before installation

By following this guide, you’ll be able to diagnose and replace your blower motor resistor with confidence, restoring proper function to your vehicle’s HVAC system while saving money on professional repairs.