* Verify the new resistor is correctly installed: Double-check the wiring connections to the new blower motor resistor. Even a slightly loose or incorrect connection can cause problems. Refer to a wiring diagram (available online through repair manuals or forums dedicated to Chevy Impalas) to ensure everything is properly connected.
* Check the blower motor itself: While less likely if the fan works on high, a failing blower motor can sometimes only function at its highest speed. Try testing the motor directly with power (carefully!) to see if it runs at lower speeds when supplied with a lower voltage. This requires some electrical knowledge and caution.
* Inspect the wiring harness: Carefully examine the wiring harness leading to the blower motor resistor and the blower motor itself. Look for:
* Broken or frayed wires: These can cause intermittent or complete loss of function at lower speeds.
* Corrosion: Corrosion on connectors can disrupt the electrical signal. Clean any corroded connectors with a wire brush and electrical contact cleaner.
* Test the switch: While you've replaced the blower motor resistor, it's possible (though less probable) there's a problem with the switch itself. A multimeter can help to test the continuity and voltage at the switch in different positions. This is more advanced troubleshooting and requires electrical testing knowledge.
* Check for blown fuses or relays: A blown fuse or relay related to the blower motor could also cause this problem. Consult your owner's manual to locate the relevant fuses and relays and test them.
* Consult a wiring diagram: A wiring diagram is essential for accurate troubleshooting. It will show you the path of the electrical circuit and help you pinpoint the exact location of potential problems.
* Seek professional help: If you're not comfortable with electrical work, it's best to take your Impala to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately and repair it safely.
The fact that it *only* works on high suggests a problem with the resistor's circuitry or its connection to the other speed settings. However, a failing blower motor or a wiring problem can't be completely ruled out. Systematic checking of each component, using a wiring diagram as a guide, is the key to resolving this.
