Summary:
Replacing a blower motor resistor module is a straightforward repair that restores multiple speeds to your car’s heater/air conditioner. With over 50 years of experience, I’ve dealt with many HVAC systems and found replacing the resistor module to be one of the simpler fixes.
How a Car Heater Fan Works
A car heater fan works by controlling voltage to the blower motor, with a resistor module regulating the current to achieve different fan speeds. When the blower motor only works on one speed, it’s often due to a defective resistor. Blower motor resistor modules, which used to rely on various coiled wires, now often use transistors in modern vehicles. These resistors adjust current flow based on the fan speed setting.
Steps to Fix a Faulty Resistor Module
- Purchase a New Module: Buy a replacement resistor module. Prices range from $25 to over $250.
- Locate the Module: It’s usually found in the heater ductwork, under the dash or near the blower motor.
- Disconnect the Battery: Always disconnect the negative battery cable before starting.
- Remove the Old Module: Disconnect the wiring harness, remove any mounting screws or clips, and slide out the old module.
- Inspect and Clean: Check for any debris blocking airflow or issues with the wiring harness. Clean terminals if necessary.
- Install the New Module: Reverse the removal process, ensuring all connections are secure and reinstall any gaskets or clips.
- Reconnect the Battery: After installation, reconnect the battery and test the fan operation.
Common Issues and Maintenance
Common issues leading to resistor failure include improper airflow, dirt or debris in the heater duct, or a blower motor drawing too many amps. If corrosion or damaged wiring is observed, the blower motor may also need replacement.
Proper maintenance, including checking and replacing the cabin air filter, can help prevent future issues.
Family Handyman
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