* Faulty Climate Control Module (CCM): This is the "brain" of the system. A malfunctioning CCM can cause erratic behavior, including only certain fan speeds or temperature settings working. This is often the most likely culprit when multiple settings are affected.
* Blend Door Actuator Problems: These motors control the direction of air (e.g., vents, defrost, floor). If one or more actuators are failing or stuck, it could limit the airflow settings. Since it's only *five* settings, a specific actuator might be partially functional or intermittently failing. They are notorious for failure in these vehicles.
* Wiring Issues: Corrosion, broken wires, or loose connections in the wiring harness leading to the actuators or CCM can interrupt signals and cause intermittent operation. Look for any signs of damage near the climate control unit and under the dashboard.
* Resistor Pack (Fan Speed Control): While it seems less likely since it's affecting temperature/airflow direction, a failing resistor pack (controls fan speeds) *could* indirectly impact other aspects of the system's operation by disrupting power flow. However, if only the fan speed was affected, this would be a more obvious suspect.
* Vacuum Leaks (Less Likely): Older vehicles sometimes use vacuum lines to control some climate functions. A leak would make the system behave erratically. However, this is less common in the climate control of a 2002 Impala.
Troubleshooting Steps (in order of likelihood):
1. Check fuses and relays: Start with the simple stuff. Ensure all relevant fuses and relays for the climate control system are intact. Consult your owner's manual for locations.
2. Inspect the Climate Control Module (CCM): This will likely require some disassembly of the dashboard. Look for any obvious signs of damage, corrosion, or loose connections. If you're not comfortable with this, a professional should handle it. Consider cleaning connections with electrical contact cleaner.
3. Diagnose Blend Door Actuators: This involves accessing the actuators (usually behind the dashboard) and checking for movement and proper operation. A scan tool may be necessary to test their functionality. If an actuator is stuck or making odd noises, replacement is often required.
4. Check wiring: Trace the wiring harness leading from the CCM to the actuators and the blower motor resistor. Look for any signs of damage, chafing, or loose connections.
5. Professional Diagnosis: If you're not comfortable with automotive electrical work, take your vehicle to a qualified mechanic or auto electrician. They'll have the tools (scanners, diagnostic software) to accurately pinpoint the problem.
Remember safety first! Disconnecting the battery before working on electrical components is crucial. If you're unsure about any step, consult a professional. The specific blend door actuators and CCM for a 2002 Impala can be expensive, so proper diagnosis is key before replacing parts.
