1. Check the Blower Motor Resistor:
* What it does: This resistor controls the different fan speeds. A faulty resistor often leads to only the highest speed working (or none at all, sometimes).
* How to check: Locate the blower motor resistor (usually under the dashboard, sometimes behind the glovebox). It's often a small, rectangular unit. Inspect it visually for burned components or loose connections. A multimeter can confirm its resistance values (though you'll need a schematic to know the correct values).
* How to fix: Replace the resistor. This is a relatively inexpensive and easy repair. Many online parts stores can provide diagrams showing its location in your specific Sunfire.
2. Check the Blower Motor Switch:
* What it does: This switch controls the fan speed settings. A faulty switch can cause intermittent operation or no operation at all.
* How to check: This is more difficult. You'll likely need to access the switch (often behind the dashboard) and test its circuits with a multimeter while operating the switch. This requires some electrical knowledge and potentially removing parts of your dashboard. It's best to consult a wiring diagram specific to your 1996 Pontiac Sunfire.
* How to fix: Replace the switch. This is more involved than replacing the resistor.
3. Check the Wiring and Connections:
* What it does: Loose, corroded, or damaged wiring can interrupt the power supply to the blower motor.
* How to check: Visually inspect all wires leading to the blower motor, the resistor, and the switch. Look for broken wires, loose connections, corrosion, or melted insulation. Use a multimeter to check for continuity in the wires.
* How to fix: Repair or replace any damaged wiring, clean corroded connections, and ensure all connections are secure.
4. Check the Blower Motor Itself (Last Resort):
* What it does: Though less likely given your description, the blower motor itself could have an internal fault causing intermittent operation.
* How to check: This involves removing the blower motor (usually requires removing parts of the dashboard or the blower housing). Once removed, you can visually inspect it for obvious damage. Testing it directly requires more specialized equipment.
* How to fix: Replacing the blower motor is the most expensive and time-consuming option.
Before you start:
* Disconnect the negative battery terminal before working on any electrical components. This is crucial for safety.
* Consult a repair manual: A repair manual specific to your 1996 Pontiac Sunfire will provide detailed diagrams and instructions for accessing and testing the components mentioned above. You can find these online or at auto parts stores.
If you're not comfortable working on electrical systems, it's best to take your car to a qualified mechanic. Diagnosing electrical problems can be tricky, and incorrectly repairing them can lead to further damage or even injury.
