How to Determine if the Blower Motor Resistor is Faulty?
2 Answers
To determine if the car's air conditioning blower motor is faulty, measure the resistance value. If the reading is infinite, it indicates an internal open circuit in the motor. If the reading is zero, it indicates an internal short circuit in the motor. A normal reading should be a specific value. Below are the specific steps for replacing the blower motor resistor: 1. Turn off electrical equipment: Prepare the replacement blower motor resistor, a Phillips screwdriver, and other tools. Turn off all electrical equipment and the ignition switch in the car. 2. Remove the fixing screws: Disconnect the car's battery and the blower assembly connector (the blower is usually located under the glove compartment in front of the passenger seat). Remove the blower's fixed wiring harness, then remove the blower assembly's fixing screws. 3. Replace the resistor: Locate the resistor (connected near the air duct) in the position where the blower was removed. Use tools to remove it and install the new resistor. 4. Reinstall: Reinstall the blower and all wiring, then reconnect the battery. Start the car and activate the blower to check if the blower's speed can be adjusted.
My car's AC fan had a similar issue before—the fan only worked at high speed while other settings didn't respond at all. It was likely a faulty blower motor resistor. That small resistor controls the fan speed, and once it fails, the airflow gets stuck at one speed. The diagnostic method is quite simple: sit in the car, turn on the AC, and cycle through different speed settings. If only the high-speed setting works while lower speeds don't respond, you can pretty much confirm it's a resistor issue. Then, turn off the engine, open the glove compartment or hood to locate the resistor (usually near the fan), and feel it with your hand—a faulty resistor often overheats or even burns to the touch. If you're worried about electric shock, don't tamper with it; it's best to use a multimeter to test the resistance—if it reads infinity or zero, it's definitely dead. Not replacing the resistor in time will drain more power and strain the fan motor. Regularly changing the AC filter can reduce dust buildup and prevent such failures—I check mine monthly, which saves a lot of hassle.
