How to Replace a Blower Motor Resistor
The blower motor resistor in your vehicle is a small but crucial component of the heating and air conditioning system. Its function is to control the speed of the blower motor, allowing you to adjust the airflow from the vents to your desired level. When this resistor fails, you might experience issues like the blower motor only working on one speed (usually high), not working at all, or working intermittently. Fortunately, replacing a blower motor resistor is a relatively straightforward DIY task that can save you money on repair costs. This comprehensive guide will walk you through the process step-by-step, providing you with the knowledge and confidence to tackle this repair yourself.
Understanding the Blower Motor Resistor
Before diving into the replacement process, it’s helpful to understand what a blower motor resistor does and how it works. The blower motor resistor is typically located in the HVAC housing, near the blower motor itself. It consists of a series of resistors that drop the voltage supplied to the blower motor. By varying the voltage, the resistor controls the speed of the motor.
Think of it like a dimmer switch for your lights. Just as a dimmer switch controls the brightness of a light bulb by regulating the electrical current, the blower motor resistor controls the speed of the blower motor by regulating the voltage.
When the resistor fails, it often breaks or burns out in one or more sections. This can result in the blower motor only working on certain speeds, as the voltage can only pass through the remaining functional resistors. In some cases, the resistor may fail completely, preventing the blower motor from working at all.
Symptoms of a Faulty Blower Motor Resistor
Recognizing the symptoms of a failing blower motor resistor is essential for diagnosing the problem correctly. Here are the most common signs:
- Blower motor only works on one speed (usually high): This is the most common symptom. The high-speed setting often bypasses the resistor, so it may be the only speed that still functions.
- Blower motor doesn’t work on certain speeds: Some speeds may work, while others don’t. This indicates that specific resistors within the unit have failed.
- Blower motor doesn’t work at all: A complete failure of the resistor can prevent the blower motor from operating on any speed.
- Blower motor works intermittently: The blower motor may turn on and off randomly, suggesting a loose connection or a failing resistor.
- Burning smell: In some cases, a burning smell may emanate from the vents, indicating that the resistor is overheating or has burned out.
Tools and Materials You’ll Need
Before you start, gather the following tools and materials:
- New blower motor resistor: Make sure to purchase the correct resistor for your vehicle’s make, model, and year. You can find this information in your owner’s manual or by contacting an auto parts store.
- Screwdrivers: You’ll likely need both Phillips-head and flat-head screwdrivers.
- Socket set: A socket set may be required to remove any bolts or nuts securing the resistor or surrounding components.
- Pliers: Pliers can be helpful for disconnecting electrical connectors.
- Multimeter (optional): A multimeter can be used to test the old resistor to confirm that it has failed.
- Work light: A work light will help you see clearly in the often-dark areas under the dashboard.
- Safety glasses: Protect your eyes from dust and debris.
- Gloves: Gloves will protect your hands from dirt and sharp edges.
- Shop towels: Keep shop towels handy for cleaning up any spills or messes.
Step-by-Step Replacement Guide
Follow these steps to replace your blower motor resistor:
1. Safety First:
- Disconnect the negative battery cable: This will prevent any electrical shorts or shocks during the repair. Locate the negative terminal on your car battery (usually marked with a "-" symbol) and use a wrench to loosen the nut securing the cable. Carefully remove the cable from the terminal and tuck it away so it doesn’t accidentally reconnect.
2. Locate the Blower Motor Resistor:
- The blower motor resistor is typically located in the HVAC housing, near the blower motor. The exact location varies depending on the vehicle’s make and model. Common locations include:
- Under the dashboard on the passenger side
- Behind the glove compartment
- Near the blower motor housing in the engine compartment (less common)
- Consult your vehicle’s repair manual or search online for specific instructions for your vehicle.
3. Access the Resistor:
- You may need to remove trim panels, the glove compartment, or other components to access the resistor. Use the appropriate screwdrivers or sockets to remove any screws or bolts securing these components.
- Be careful when removing trim panels, as they can be fragile and easily broken. Use a trim panel removal tool if available.
4. Disconnect the Electrical Connector:
- Once you have access to the resistor, you’ll see an electrical connector plugged into it. Gently disconnect the connector by pressing on the release tab (if there is one) and pulling the connector straight out.
- Do not pull on the wires themselves, as this can damage the connector or wires.
5. Remove the Old Resistor:
- The resistor is typically held in place by screws or bolts. Use the appropriate screwdrivers or sockets to remove these fasteners.
- Carefully remove the old resistor from its mounting location.
6. Install the New Resistor:
- Install the new resistor in the same location as the old one.
- Secure the resistor with the screws or bolts you removed earlier. Make sure the resistor is properly seated and that the fasteners are tightened securely.
7. Reconnect the Electrical Connector:
- Plug the electrical connector back into the new resistor. Make sure the connector is fully seated and that the release tab (if there is one) clicks into place.
8. Reassemble the Components:
- Reinstall any trim panels, the glove compartment, or other components that you removed earlier.
- Make sure all fasteners are tightened securely.
9. Reconnect the Negative Battery Cable:
- Reconnect the negative battery cable to the negative terminal on your car battery. Tighten the nut securing the cable.
10. Test the Blower Motor:
- Turn on the ignition and test the blower motor on all speeds. Make sure the blower motor is working properly on all settings.
11. Final Check:
- Double-check that all components are properly installed and that all fasteners are tightened securely.
- Clean up any tools or materials you used during the repair.
Troubleshooting
If the blower motor still doesn’t work after replacing the resistor, here are some potential causes:
- Blown fuse: Check the fuse for the blower motor. It may have blown due to the faulty resistor. Replace the fuse with one of the same amperage.
- Faulty blower motor: The blower motor itself may be faulty. You can test the blower motor by applying direct power to it. If it doesn’t turn on, the motor needs to be replaced.
- Wiring issue: There may be a wiring problem in the circuit. Check for any damaged or corroded wires.
- Faulty blower motor switch: The blower motor switch may be faulty. You can test the switch with a multimeter.
Tips for Success
- Take pictures: Before removing any components, take pictures of their locations. This will help you remember how to put everything back together.
- Keep track of screws and bolts: Place screws and bolts in a container or labeled bag to avoid losing them.
- Don’t force anything: If a component is difficult to remove, double-check that you have removed all the necessary fasteners. Forcing a component can damage it or surrounding parts.
- Consult a professional: If you are unsure about any part of the repair process, consult a qualified mechanic.
Conclusion
Replacing a blower motor resistor is a manageable task for the average DIYer. By following these steps, you can save yourself a significant amount of money on repair costs. Remember to always prioritize safety and to consult a professional if you have any doubts. With a little patience and the right tools, you can get your vehicle’s heating and air conditioning system working properly again.
