Here's a breakdown of why:
* Blower Motor Resistor: This resistor controls the different fan speeds. When it fails, it often defaults to the highest speed because the resistor's pathway is essentially bypassed. This is the most common cause.
* Blower Motor Control Module (Often part of the Resistor): This module receives signals from the climate control system to adjust the fan speed. A faulty module can cause the fan to run constantly at high speed, or not at all. In many Chrysler vehicles, this is integrated into the resistor assembly.
* Short Circuit in Wiring: Less likely, but possible. A short circuit in the wiring harness leading to the blower motor or its control unit could also cause the motor to run continuously at full speed. This often involves damage to the wiring itself.
* Faulty Blower Motor Switch: While less frequent, a problem with the switch itself could also cause a malfunction. However, this usually results in the fan not working at all, or not responding to speed changes, rather than continuously running on high.
What to do:
1. Check the fuses: Before anything else, check the fuses related to the blower motor and climate control system. A blown fuse could initially seem unrelated but could indicate a larger underlying problem.
2. Locate the Blower Motor Resistor: This is usually located behind the glove compartment (sometimes under the dashboard) or near the blower motor itself. Consult your repair manual or online resources for the exact location in your vehicle. Inspect it visually for any signs of burning, melting, or other damage. Often, you'll see several burned-out resistors. This is a strong indicator of the problem.
3. Replace the Blower Motor Resistor (and possibly the module): Since this is the most likely culprit, replacing the resistor is often the first step in resolving this issue. This is a relatively straightforward repair for many car enthusiasts but may require some patience and basic mechanical skills. The resistor pack often contains the module, so replacement usually entails replacing the entire unit.
Important Note: If you're not comfortable working on your car's electrical system, it's best to take it to a qualified mechanic. Improperly handling electrical components can lead to further damage or even injury. A professional will be able to diagnose the problem accurately and perform the necessary repairs safely.
