Here's what you should check:
* Blower Motor Resistor: This is the most common culprit. It's usually located behind the glove box or under the dash, near the blower motor. Access it, visually inspect it for any obvious signs of damage (burning, melting), and check for continuity with a multimeter. If it's burnt or shows no continuity, it needs replacement.
* Wiring and Connections: While less likely than a bad resistor, inspect the wiring harness connected to the resistor and the blower motor itself. Look for any loose connections, broken wires, or corrosion. A multimeter can help check for continuity and voltage at these points.
* Blower Motor: Though less frequent, a failing blower motor can sometimes manifest as only high speed working. However, this is usually accompanied by other symptoms like unusual noise or the motor not running at all.
* Fuse: Check the fuse associated with the blower motor in the fuse box. A blown fuse will prevent the blower from working at all speeds.
To fix the issue:
1. Identify the blower motor resistor: Consult a repair manual specific to your 1998 Dodge Ram van to pinpoint its location. Online forums dedicated to Dodge Ram vans might also have pictures or videos showing the resistor's location.
2. Replace the blower motor resistor: Once located, purchase a replacement resistor from an auto parts store. Be sure to get the correct part number for your specific van model.
3. Repair or replace wiring: If you find damaged wiring, repair it with proper automotive wire and connectors. If the damage is extensive, replacement of the harness section might be necessary.
4. Test the blower motor: After replacing the resistor or repairing wiring, test all speed settings to verify the repair.
If you're uncomfortable working on your vehicle's electrical system, it's best to take it to a qualified mechanic. Improperly working with car electrical systems can be dangerous.
