Here's a breakdown of why and what you can do:
* How the Resistor Pack Works: The resistor pack reduces the voltage going to the blower motor. Speed 4 usually runs directly from the battery's full voltage, bypassing the resistor pack entirely. Lower speeds use the resistor to lower the voltage and thus the speed. A faulty resistor means the lower voltage paths are broken.
* Possible Causes:
* Failed Resistor Pack: This is the most likely culprit. One or more of the resistors within the pack has burned out.
* Wiring Issues: A loose connection, broken wire, or corroded connector in the wiring leading to or from the resistor pack could be the problem.
* Blower Motor Issues (Less Likely): While less probable given that speed 4 works, a partially failed blower motor could be contributing if it requires more voltage to start than it does to keep running.
What You Can Do:
1. Check the Fuse (if applicable): Some vehicles have a fuse specifically for the blower motor or the blower motor resistor. Check your vehicle's owner's manual to locate the fuse box and check for a blown fuse.
2. Locate the Blower Motor Resistor: This is usually located behind the glove box, under the dashboard, or near the blower motor itself. Consult your vehicle's repair manual or online resources (like repair manuals specific to your make and model) to find its exact location.
3. Inspect the Resistor Pack: Once located, visually inspect the resistor pack for any signs of burning, melting, or discoloration.
4. Check the Wiring: Examine the wiring connections to and from the resistor pack for any loose connections, broken wires, or corrosion.
5. Test the Resistor Pack (Advanced): This requires a multimeter. You can test the resistance of each resistor within the pack to see if they're within their specified ranges (found in a repair manual or online). However, this step is more challenging for someone without electronics experience.
6. Replace the Resistor Pack: If you find a problem with the resistor pack or wiring, replacing it is usually the most straightforward solution. You can purchase a replacement resistor pack at an auto parts store; make sure to get the correct one for your vehicle's make, model, and year.
Important Note: If you're not comfortable working on car electrical systems, it's best to take your vehicle to a qualified mechanic. Improperly working with car electrical systems can be dangerous.
