Here's why:
* Blower Motor Resistor Function: The resistor is a variable resistance that reduces the voltage going to the blower motor. Lower speeds require lower voltage, achieved by the resistor diverting some of the power. High speed usually runs directly from the battery voltage, bypassing the resistor.
* Resistor Failure: The resistor can overheat and fail, causing the internal connections to break. This leaves only the high-speed circuit functional. Sometimes the resistor just gets dirty and its resistance changes which also causes the problem.
* Other possibilities (less likely): While less probable given the symptom, there could be issues with:
* Blower Motor itself: Though less likely, a failing blower motor *could* cause this, especially if it draws excessive current and only functions properly under the full power of the high speed setting.
* Wiring: Damaged or corroded wiring between the resistor and the blower motor, or the switch, could also cause this.
Troubleshooting Steps:
1. Check the fuse: While unlikely to be the sole cause of this issue (it would likely cause complete failure), check the fuse related to the blower motor.
2. Locate the blower motor resistor: This is usually located behind the glove box or under the dashboard. Access is often tricky and might require some disassembly. Look for a small rectangular or cylindrical component with multiple wires attached.
3. Inspect the resistor: Visually inspect the resistor for any obvious signs of damage, such as burning, melting, or loose connections. If it looks burned, it's likely the culprit.
4. Test the resistor (advanced): You could use a multimeter to test the resistance across the terminals of the resistor. The exact resistance values depend on the resistor design, and you would need a schematic to check against.
5. Check wiring: Carefully inspect the wiring going to and from the resistor for any breaks, corrosion, or loose connections.
Solution:
If you find a faulty resistor, you'll need to replace it. You can typically find replacement blower motor resistors for your specific model year at auto parts stores or online. Replacing it is generally straightforward, but access can be challenging, requiring patience and potentially some disassembly of your dashboard. If you're uncomfortable with car repair, taking it to a mechanic is a better option.
