* Blower Motor Resistor: This is the most frequent cause. The resistor controls the different fan speeds. If it's failing, it can lead to inconsistent or intermittent operation, particularly on lower speeds. Sometimes, the resistor completely fails, resulting in only the highest speed working (if at all).
* Wiring and Connections: Corrosion, loose connections, or broken wires in the blower motor circuit can interrupt the power supply, leading to intermittent operation. Check all connections, particularly at the resistor and the blower motor itself. Look for signs of corrosion or damage.
* Blower Motor itself: Although less common than resistor issues, the blower motor can malfunction intermittently. Worn brushes, a failing motor winding, or a problem with the motor's internal components can cause this.
* Switch: The blower motor switch itself can sometimes be the source of the problem, either due to internal wear or a faulty connection.
* Fuse: While less likely to cause *intermittent* problems, a failing fuse can sometimes cause erratic behavior before it completely blows. Check the fuse related to the blower motor.
* Relay: Some Cadillac models use a relay in the blower motor circuit. A faulty relay can cause intermittent operation.
Troubleshooting Steps:
1. Check the fuses: Start by examining the fuse(s) related to the blower motor in the fuse box (usually under the hood or in the interior).
2. Inspect the blower motor resistor: This is often located behind the glove box or under the dash. It's usually a relatively easy component to access and replace. Look for any signs of burning or damage.
3. Examine the wiring: Carefully inspect all wiring connected to the blower motor, resistor, and switch for any signs of damage, corrosion, or loose connections.
4. Test the blower motor: If you can access the blower motor, you can test it directly with a multimeter to verify if it's receiving power and functioning correctly (this requires some electrical knowledge).
5. Test the blower motor switch: This requires more advanced diagnostics and often involves using a multimeter to check for continuity and proper voltage at different switch positions.
6. Check the relay (if applicable): If your vehicle uses a relay for the blower motor, test the relay for proper operation.
If you're not comfortable working with car electrical systems, it's best to take your Cadillac DeVille to a qualified mechanic for diagnosis and repair. Improperly diagnosing and repairing electrical issues can be dangerous.
