* Blower Motor Resistor: This is the most common cause. The resistor controls the fan's speed. If it's failing, it may intermittently provide power to the motor, leading to the fluctuating airflow. The resistor often gets hot and can even melt.
* Blower Motor: The blower motor itself might be failing. Worn brushes or a failing motor could cause the motor to struggle at higher speeds. The increase in speed might briefly overcome the problem, but then the motor loses power.
* Wiring and Connections: Check the wiring harness and connections to the blower motor and resistor. Corrosion, loose connections, or broken wires can interrupt power and cause inconsistent airflow.
* HVAC Blower Module: This is less common, but a faulty HVAC blower module (sometimes called a control module) could be sending inconsistent signals to the blower motor.
* Debris in the Blower: Less likely, but a significant amount of debris blocking the blower wheel could restrict airflow, causing the motor to strain and cycle on and off.
Troubleshooting Steps:
1. Check the Blower Motor Resistor: This is the easiest and cheapest thing to check first. Locate the resistor (often under the dash, sometimes near the blower motor) and visually inspect it for signs of burning or damage. If it's visibly damaged, replace it. This is often a simple DIY repair.
2. Listen Carefully: As you cycle through the fan speeds, listen closely to the blower motor. Is there a grinding or whining sound? This could indicate a failing motor.
3. Check Wiring and Connections: Visually inspect the wiring harness going to the blower motor and resistor for any damage or loose connections. Reconnect any loose connectors securely.
4. Access the Blower: If possible (requires some disassembly), access the blower motor and check the blower wheel for obstructions.
5. Professional Diagnosis: If you're not comfortable checking the components yourself, take your Silverado to a qualified mechanic or auto electrician for a proper diagnosis. They have the tools and expertise to identify the exact problem.
The resistor is the most likely suspect given your description, but don't rule out the other possibilities. A proper diagnosis will prevent unnecessary parts replacements.
