* Resistor: The blower motor resistor is a common failure point. It controls the fan speeds. A faulty resistor can cause the fan to run constantly at its highest speed or simply refuse to turn off. This is a relatively easy and inexpensive part to replace.
* Blower Motor Switch: The switch itself might be malfunctioning. It could be stuck in the "on" position or have an internal short. Replacing the switch is more involved than the resistor, but still a relatively straightforward repair.
* Wiring Harness: There could be a short circuit or damaged wiring in the harness leading to the blower motor, the resistor, or the switch. Inspect the wiring carefully for any fraying, melting, or loose connections. A short in the wiring could also cause a fuse to blow repeatedly.
* Blower Motor: Though less likely to cause the fan to run *constantly*, a failing blower motor could sometimes stick on. However, a bad blower motor typically presents as inconsistent operation or no operation at all.
* Control Module (less likely): In some cases, a faulty control module (part of the climate control system) could be the problem. This is less common, but possible, and usually requires a diagnostic scan to confirm.
Troubleshooting Steps:
1. Check the fuses: Locate the fuse(s) related to the blower motor and the AC system in your fuse box (usually under the hood). Check for blown fuses. Replace any blown fuses, but be wary of a fuse blowing repeatedly as this indicates an underlying problem (short circuit).
2. Test the blower motor resistor: Access the resistor (usually located behind the glove box or under the dash). Visually inspect it for any signs of damage. You might need to use a multimeter to test its resistance values to confirm if it's faulty.
3. Inspect the wiring: Carefully examine the wiring harness connecting the blower motor, resistor, and switch. Look for any signs of damage, corrosion, or loose connections. Repair or replace any damaged wiring.
4. Test the blower motor switch: This is more difficult without specialized tools. You might need to use a multimeter to test the switch's continuity in different positions.
5. Consider a professional diagnosis: If you're uncomfortable working with electrical components or can't find the problem after checking these things, take your Jeep to a qualified mechanic or auto electrician. They have the tools to properly diagnose the issue.
Remember to disconnect the negative battery terminal before working on any electrical components in your vehicle. Safety first!
