* Blower Motor Resistor: This is the most frequent cause. The resistor is a component that regulates the speed of the blower motor. If it fails, you often lose lower speeds, while the highest speed might still work (though sometimes even that fails as well). The resistor is usually located behind the glove box or under the dash. It's relatively inexpensive and easy to replace, though access can be tricky depending on the vehicle make and model.
* Blower Motor itself: While less common than a resistor failure, the blower motor itself could be failing. Worn brushes or a failing motor can lead to loss of speeds. Replacing the blower motor is a more involved repair, potentially requiring more disassembly.
* Wiring and Connections: A loose, corroded, or broken wire in the blower motor circuit can interrupt the lower speed settings. Check all connections and wiring leading to the blower motor and resistor.
* Switch (blower control): A faulty blower motor switch could also be the problem. This is less likely than a resistor issue, but possible. Sometimes cleaning the switch contacts might resolve intermittent problems.
* Fuse: Check your vehicle's fuse box for a blown fuse related to the blower motor. This is a quick and easy check to rule out.
To diagnose the problem:
1. Check the fuses: Locate the blower motor fuse in your fuse box (consult your owner's manual).
2. Inspect the blower motor resistor: This is usually the most likely culprit. Access it and visually inspect it for any obvious signs of damage (burnt components).
3. Check wiring and connectors: Look for any loose, corroded, or broken wires in the circuit.
4. Test the blower motor itself (advanced): This requires some electrical testing knowledge and tools. You'd need to access the motor and test its voltage and current draw.
Without knowing the *make and model* of your 1999 vehicle, it's impossible to give more specific guidance. Consult your owner's manual or a repair manual specific to your vehicle. Searching online for "[Your Vehicle Make and Model] blower motor resistor replacement" will likely yield helpful videos and guides.
If you're not comfortable working on your car's electrical system, it's best to take it to a qualified mechanic. Replacing the resistor is usually a cost-effective repair, while a motor replacement can be more expensive.
