Here's why and what to do:
* How the resistor works: The blower motor resistor is a variable resistor that reduces the voltage going to the blower motor. Each speed setting on your control panel sends power through a different part of the resistor, changing the resistance and thus the voltage, and consequently the motor speed. When the resistor fails, the highest speed setting usually still works because it bypasses the resistor altogether.
* Troubleshooting: Before replacing parts, try these things:
* Check the fuses: Although less likely to be the problem if only high speed works, it's always a good idea to check all fuses related to the blower motor in your fuse box.
* Inspect the blower motor switch: While less common, a faulty blower motor switch could cause this issue. However, it's usually more of a problem with multiple speeds not working.
* Replacement: If the fuses are fine, and you've tested your switch, the most probable solution is to replace the blower motor resistor. This is usually a relatively inexpensive and easily accessible part. You can find a replacement at most auto parts stores. There are many online videos that show how to locate and replace the resistor for a 2000 Ford Ranger. Be sure to specify your year and model when searching for a replacement.
Important Note: While the resistor is the most likely culprit, it's always possible (though less probable in this case) that there's a wiring problem or even a failing blower motor itself. If replacing the resistor doesn't solve the issue, further diagnosis might be necessary.
