* Blocked Airflow: This is the most common cause. Check these areas:
* Cabin Air Filter: A clogged cabin air filter restricts airflow dramatically. This is the easiest and cheapest thing to check first. Locate it (usually under the dashboard or glove compartment) and replace it if necessary.
* Evaporator Core: This component is located behind the dashboard and can become clogged with debris or restricted by ice buildup (especially if the AC is used frequently). This requires more significant disassembly to check.
* Vents and Ducts: Check the vents themselves for obstructions. Debris, leaves, or even something like a toy could be blocking air passage. More importantly, there's a whole system of ducts behind the dash; a blockage anywhere in that system will reduce airflow. This is difficult to diagnose without specialized tools or a service manual.
* Blend Door Actuators: These small motors control the direction of airflow (e.g., dash, floor, defrost). A malfunctioning blend door actuator could be partially blocking airflow.
* Vacuum Leaks: The HVAC system in some vehicles uses vacuum to control airflow direction. A leak in the vacuum lines can disrupt this control, potentially limiting airflow even if the blend doors are functioning.
* Blend Door Problems: Even if the actuators are working, the blend doors themselves might be broken or stuck in a partially closed position.
* Blower Motor Resistor: While you say the fan works at all speeds, a failing resistor could still contribute to reduced airflow *despite* the fan running. A faulty resistor may not be providing the correct voltage to the fan motor at all speeds, resulting in a lower air flow despite seeming to work correctly.
* Leaking or Damaged Ducts: Over time, the ductwork can become detached or develop holes, leading to air loss before it reaches the vents. This is more difficult to diagnose without professional help.
Troubleshooting Steps:
1. Check the cabin air filter FIRST. This is the easiest and cheapest fix.
2. Inspect the vents visually for any obvious obstructions.
3. Listen carefully: Are there any unusual noises (rattling, hissing) coming from the dashboard area when the HVAC is on? This might indicate a problem with the ducts or actuators.
4. Test the HVAC system with the AC on and off. See if the airflow changes significantly. Reduced airflow with the AC on might suggest a frozen evaporator core.
5. If you're comfortable working on cars, you might try inspecting the accessible portions of the ductwork.
If you're not mechanically inclined, it's best to take your Silverado to a qualified mechanic for diagnosis and repair. The problem could be relatively minor (a clogged filter) or quite involved (a damaged evaporator core or ductwork). Attempting complex repairs without experience could lead to further damage.
