1. Check the Fuses: Start with the easiest. Your owner's manual will show you the fuse box location and diagram. Look for fuses related to the blower motor, HVAC system, or accessories. Replace any blown fuses.
2. Check the Blower Motor Resistor: This component controls the fan speeds. A faulty resistor can cause the blower to not work at all, or only on the highest setting (if at all). This is a common failure point on many vehicles. The location varies by model year, so consult a repair manual or online forum specific to your 1998 Cadillac DeVille to find its location. It's usually located under the dashboard or near the blower motor itself. You can visually inspect it for obvious damage (burn marks, etc.) and test it with a multimeter if you have one.
3. Check the Blower Motor Switch: The switch itself could be faulty. Try cycling through all the fan speeds multiple times. A failing switch might make intermittent contact. Replacing this involves some dashboard disassembly.
4. Check the Blower Motor: This is the most expensive and difficult to replace. Accessing it often requires significant disassembly of the dashboard or under-dash area. You can test it directly with a multimeter (bypassing the resistor and switch) to see if it receives power and if it's functioning. If it's bad, you'll need a replacement.
5. Check Wiring and Connections: Inspect the wiring harness leading to the blower motor, resistor, and switch for any loose, broken, or corroded connections. Repair or replace as needed.
6. Check the HVAC Control Module: This is a more advanced step and might require a scan tool. The module controls the entire HVAC system, and a fault within it could prevent the blower motor from functioning.
7. Consult a Repair Manual: A repair manual specific to your 1998 Cadillac DeVille will provide detailed diagrams, procedures, and component locations. This is extremely helpful for more involved troubleshooting and repairs.
8. Seek Professional Help: If you're not comfortable with electrical work or dashboard disassembly, it's best to take your car to a qualified mechanic. They have the tools and experience to diagnose and repair the problem efficiently.
Remember safety first! Disconnect the negative battery terminal before working on any electrical components. If you're not comfortable with electrical repairs, it's advisable to have a qualified mechanic handle the diagnosis and repair.
