* Rheostat (Blower Motor Resistor): This is the most common culprit. The rheostat is a resistor pack that controls the different fan speeds. If it's faulty, it might only allow current to flow through the lower speed settings. A failed resistor often causes the higher speeds to not function, but still allow the lowest speed(s) to work. This is because the low speeds may bypass part of the resistor network.
* Blower Motor Switch: The switch itself could be failing. While less common than the rheostat problem, a faulty switch could be preventing the higher speeds from activating. It's possible a poor connection inside the switch is only making contact with the lowest speeds.
* Wiring Issues: Broken, corroded, or loose wires in the circuit leading to the blower motor or the resistor can interrupt power at higher speeds. This is less common but could be the source.
* Blower Motor Itself: While less likely given that the low speeds work, a failing blower motor could be drawing too much current, causing the higher speeds to fail due to a blown fuse or tripped breaker (though a blown fuse/breaker would typically result in no fan operation at all). However, a partially-failing motor might work at low speeds but struggle at higher ones.
* Fuse/Circuit Breaker: Check your fuse box or circuit breaker panel. A blown fuse or tripped breaker can cut power to the entire blower motor circuit or only specific speeds if there's a specialized fuse/breaker for certain speeds.
Troubleshooting Steps:
1. Check the fuses/circuit breakers: This is the easiest first step. Consult your owner's manual to locate the correct fuse(s) or breaker(s).
2. Locate the blower motor resistor: This is usually found under the dash, sometimes near the blower motor itself, or tucked away behind panels. Access varies depending on the model, so you may need to consult a repair manual or online resources specific to your 1999 Chevy Malibu. Visually inspect it for any obvious damage, such as burning or melted components. Replacing this is often a relatively inexpensive and easy fix.
3. Check the blower motor switch: This is located on the climate control panel. While less likely to be the problem, it is possible to test its continuity with a multimeter if you have one. However, replacing the whole switch is often more practical than trying to repair it.
4. Inspect wiring: Once you have access to the resistor and the blower motor, carefully inspect the wiring harness for any obvious damage, corrosion, or loose connections.
If you're not comfortable working on your car's electrical system, it's best to take it to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately and efficiently.
