* Blower Motor Resistor: This is the most frequent culprit. The resistor controls the different fan speeds. If it fails, the motor often defaults to high speed. The resistor is usually located behind the glove box or under the dash. It's a relatively inexpensive and easy part to replace.
* Blower Motor Control Module (Blower Motor Control Unit - BMCU): This module receives signals from the climate control system and sends the appropriate power to the blower motor to regulate speed. If it malfunctions, it might send a constant high-speed signal. This is less common than a bad resistor but still possible.
* Wiring Issues: A short circuit or damaged wiring in the circuit leading to the blower motor could bypass the resistor and send full power to the motor. This requires more investigation to trace the wiring.
* Faulty Blower Motor: While less likely than the other issues, a failing blower motor itself *could* cause it to run constantly at full speed. This is usually accompanied by other symptoms like unusual noises or intermittent operation.
Troubleshooting Steps:
1. Check the Blower Motor Resistor: This is the easiest and cheapest place to start. Look up a repair video for your specific year and model Explorer on YouTube to find its location and how to replace it.
2. Inspect the Wiring: Carefully examine the wiring harness leading to the blower motor and the resistor for any signs of damage, fraying, or shorts.
3. Advanced Diagnostics: If the above steps don't solve the problem, you might need a professional mechanic or an OBD-II scanner to diagnose more complex issues with the BMCU or other control modules.
Before attempting any repairs, disconnect the negative battery terminal to prevent electrical shocks. If you're not comfortable working on your vehicle's electrical system, it's best to take it to a qualified mechanic.
