Here are the most likely culprits:
* Loose or Corroded Connections: Check all the electrical connections related to the blower motor. This includes the connections at the blower motor resistor (located behind the glove box in most DeVille models), the blower motor itself, and the wiring harness leading to these components. Look for corrosion, loose wires, or broken connectors. Pay close attention to connections that might vibrate loose.
* Faulty Blower Motor Resistor: This component regulates the fan speed. A failing resistor can cause intermittent operation, and the shaking from the door slam might be momentarily restoring contact within a failing part.
* Faulty Blower Motor Switch: While less likely given the door slam effect, a failing switch can also lead to intermittent blower operation. However, this is less likely since slamming the door is directly influencing the system.
* Wiring Harness Issues: A break or short in the wiring harness running to the blower motor or resistor can create intermittent issues. This might involve a damaged wire from age, or wear from flexing near the door jamb.
Troubleshooting Steps:
1. Check the obvious: Begin by carefully inspecting all the wiring connections mentioned above. Clean any corrosion with a wire brush and electrical contact cleaner. Secure any loose connections.
2. Access the Blower Motor Resistor: Locate the blower motor resistor (usually behind the glove box). Inspect it for any signs of damage or burning. This often requires removing the glove box or some trim pieces. A visual inspection might reveal a loose connection, burnt area or even a broken resistor.
3. Test the Blower Motor (advanced): If you have some electrical testing experience, you can test the blower motor directly using a multimeter to check for continuity and proper voltage at the motor. This is more involved but can definitively rule out the motor itself as the source of the issue.
4. Professional Diagnosis: If you're uncomfortable working with car electrical systems, taking your DeVille to a qualified mechanic or auto electrician is the best approach. They have the tools and experience to diagnose and repair the issue efficiently.
The door slam is a major clue, indicating a very loose or intermittent connection somewhere in the circuit, likely near the passenger side. Focus your attention on areas subjected to vibration and movement near that door.
