Understanding Blower Motor Resistors: How They Work and Why They Fail

Understanding Blower Motor Resistors: How They Work and Why They Fail

Blower motor resistors are an essential component of modern automotive and HVAC systems. These resistors help control the speed of the blower motor fan, which is responsible for circulating air through the heating, ventilation, and air conditioning (HVAC) system. Without a functioning blower motor resistor, the fan may not work at all, or it may be stuck on a single speed.

In this article, we will explore how blower motor resistors work, the different types of resistors available, and why they sometimes fail.

How Blower Motor Resistors Work

Blower motor resistors work by regulating the amount of electrical current that flows through the fan motor. This is achieved by varying the resistance of the resistor. The higher the resistance, the less current that flows through the motor, which results in a slower fan speed. Conversely, the lower the resistance, the more current that flows, resulting in a higher fan speed.

 

Blower motor resistors are usually located in the HVAC system’s air ducts, close to the blower motor fan. They are typically made up of several resistors connected in series, each with a different resistance value. By selecting different resistors in the circuit, the fan speed can be controlled.

Types of Blower Motor Resistors

There are several types of blower motor resistors available, each with its unique features and benefits. The most common types include:

1. Thermal Fuse Resistor

Thermal fuse resistors are designed to protect the blower motor from overheating. If the fan motor draws too much current, the thermal fuse will trip, cutting off the power to the motor. This prevents damage to the motor and the rest of the HVAC system.

2. Wire Wound Resistor

Wire wound resistors are made by winding a wire around a ceramic core. They are rugged and can handle high current loads. Wire wound resistors are commonly used in HVAC systems with high power requirements.

3. Ceramic Resistor

Ceramic resistors are made of a ceramic material that has been coated with a conductive material. They are commonly used in automotive applications due to their compact size and ability to handle high temperatures.

4. Printed Circuit Board (PCB) Resistor

PCB resistors are made by depositing a thin layer of conductive material onto a printed circuit board. They are compact and can be manufactured in large quantities, making them an affordable option for HVAC systems with low to medium power requirements.

Why Blower Motor Resistors Fail

Blower motor resistors can fail for several reasons, including:

1. Overheating

Blower motor resistors are exposed to high temperatures from the HVAC system, which can cause them to overheat and fail.

2. Electrical Overload

If the blower motor draws too much current, it can overload the resistor, causing it to fail.

3. Corrosion

Corrosion can build upon the contacts of the blower motor resistor, leading to poor electrical contact and eventual failure.

4. Age

Over time, blower motor resistors can degrade, leading to reduced performance and eventual failure.

Common Signs of a Faulty Blower Motor Resistor in Your Vehicle

A blower motor resistor is a small but important component in your vehicle’s HVAC system. It’s responsible for controlling the speed of the blower motor, which in turn determines the airflow inside the cabin. When the blower motor resistor fails, it can cause a range of problems that can be frustrating and uncomfortable for passengers. Here are some common signs of a faulty blower motor resistor in your vehicle.

1. Blower Motor Only Works on High: If your blower motor only works on the highest speed setting, it’s likely that the blower motor resistor is failing. This is because the high-speed setting bypasses the resistor, which means that it’s the only setting that can still work when the resistor is faulty.
2. Limited Airflow: Another common sign of a failing blower motor resistor is limited airflow. If the blower motor resistor is failing, it won’t be able to regulate the speed of the blower motor properly, which can result in reduced airflow inside the cabin.
3. No Airflow: If the blower motor resistor fails completely, it can cause the blower motor to stop working altogether. This means that there will be no airflow inside the cabin, which can be a major problem, especially during extreme weather conditions.
4. Burnt Smell: If the blower motor resistor overheats, it can produce a burnt smell inside the cabin. This is because the resistor is designed to dissipate heat, and if it can’t do so properly, it can overheat and potentially cause a fire.
5. Strange Noises: A faulty blower motor resistor can also cause strange noises to come from the HVAC system. This can be caused by the blower motor running at a higher speed than usual, or by the blower motor struggling to maintain a consistent speed due to the failing resistor.

In summary, a faulty blower motor resistor can cause a range of problems in your vehicle’s HVAC system, including limited or no airflow, strange noises, and even a burnt smell. If you’re experiencing any of these issues, it’s important to have your vehicle inspected by a qualified technician to determine the cause and make any necessary repairs.

The blower motor resistor is a crucial component of your vehicle’s HVAC system. It regulates the speed of the blower motor, which controls the airflow inside the cabin. However, the factory-installed resistor may not always meet your specific needs, especially if you frequently use your vehicle’s HVAC system. Upgrading your blower motor resistor can offer several benefits, but it’s important to consider the following factors before making any modifications.

Benefits of Upgrading Your Blower Motor Resistor

1. Improved Efficiency: Upgrading your blower motor resistor can result in improved efficiency of the HVAC system. This is because aftermarket resistors are often designed to reduce the power consumption of the blower motor, which can result in better fuel efficiency and reduced wear and tear on the system.
2. Increased Airflow: Aftermarket blower motor resistors can provide increased airflow inside the cabin. This is because they often allow for greater control over the speed of the blower motor, which can result in more air being circulated throughout the cabin.
3. Enhanced Durability: Upgrading your blower motor resistor can result in a more durable and longer-lasting component. Aftermarket resistors are often made with higher quality materials than factory-installed resistors, which can help prevent premature failure and reduce the need for frequent replacements.

Considerations Before Upgrading Your Blower Motor Resistor

1. Compatibility: It’s important to ensure that the upgraded blower motor resistor is compatible with your specific vehicle make and model. This can be determined by consulting with a qualified technician or reviewing the manufacturer’s specifications.
2. Wiring and Installation: Upgrading your blower motor resistor may require additional wiring or modifications to the existing wiring harness. It’s important to ensure that the installation is done properly to prevent any electrical issues or potential damage to the system.
3. Warranty and Insurance: Modifying the HVAC system of your vehicle may void the manufacturer’s warranty or insurance coverage. It’s important to review your warranty and insurance policies before making any modifications to ensure that you are not risking coverage.

Conclusion

Blower motor resistors are a critical component of modern HVAC systems. They allow for the precise control of fan speed, ensuring that the HVAC system operates efficiently and effectively. By understanding how blower motor resistors work, the different types available, and why they sometimes fail, you can take steps to keep your HVAC system running smoothly. If you suspect that your blower motor resistor is faulty, it’s essential to have it inspected and repaired by a qualified technician to ensure safe and reliable operation.