Owner's Problem Description
The owner reports that the AC was functioning well until they stopped at a store. Upon restarting the vehicle, a loud rumbling noise emerged from the AC system, similar to something being stuck. This noise persists when the heater is turned on. The owner suspects the blower motor or the resistor relay might be at fault but is uncertain. They also feel a slight vibration when placing a hand under the dash near the passenger side.
Professional Technical Analysis
The 2010 Chevrolet Avalanche features a climate control system that includes both AC and heating functions. In this case, the owner reports a loud rumbling noise when the AC is activated, indicating a potential issue with the blower motor or associated components. Given the vehicle's age (approximately 13 years old) and its likely mileage (estimated at 100,000+ miles), component wear or debris accumulation within the blower motor assembly is plausible. When the vehicle was restarted after a brief stop, the noise suggests that something may have interfered with the blower fan operation. The interconnection of the blower motor and the HVAC control module is critical here, as a malfunction in the motor can lead to improper airflow and may also trigger related diagnostic codes in the PCM. The noise level increasing with fan speed typically indicates a physical obstruction or mechanical failure. Additionally, the slight vibration felt by the owner may correlate with the blower motor's operational status, pointing towards a failing bearing or motor assembly. This situation requires thorough investigation to prevent further damage to the HVAC system and ensure safe operation. It's advisable to perform an inspection of the blower motor assembly for foreign objects, inspect the electrical connections, and check for any related fault codes using an OBD-II scanner like the GeekOBD APP.
Possible Causes
Most common causes (ordered by frequency):
- Foreign Object in Blower Motor: The rumbling noise may indicate that a piece of debris, such as tape or insulation, has become lodged in the blower motor impeller. This can cause vibrations and increased noise levels, especially at higher fan speeds. The blower motor should be inspected for any obstructions, and proper operation should be verified to ensure that airflow is not restricted. - Audible rumbling noise from the passenger side, increased noise at higher fan settings, slight vibration felt in the same area.
- Blower Motor Failure: The blower motor itself may be failing, leading to increased noise and vibrations. A worn-out bearing or internal component failure can cause the motor to struggle under load, producing unusual sounds. Testing the motor’s resistance and operational integrity is recommended to confirm its functionality. - Increased noise when operating AC or heater, possible vibration when touching the area near the blower motor.
- Resistor Relay Issue: If the blower motor resistor relay is malfunctioning, it may cause irregular power delivery to the blower motor, resulting in abnormal operational noise. Inspecting the relay for proper function and checking for any burnt connections or corrosion is essential. - Unusual noise patterns correlating with fan speed settings, potential history of HVAC system issues.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial Inspection: Begin by inspecting the area under the dashboard, particularly around the passenger side where the noise is reported. Look for any visible obstructions in the blower motor area. If possible, remove the lower dash panel to gain better access. This step can help identify any foreign objects causing the noise and vibration.
- STEP 2 - Functional Testing: Use the GeekOBD APP to perform an OBD-II scan and check for any related fault codes that may indicate issues with the blower motor or HVAC system. Additionally, engage the blower at various speed settings to monitor noise changes and operational behavior.
- STEP 3 - Electrical Testing: With the blower motor accessible, perform a resistance check on the motor windings (should be between 0.5-5 ohms). Also, check the blower motor relay for correct operation and any signs of overheating or burnt connections. This will help confirm if the motor is operational.
- STEP 4 - Road Test: After performing the necessary inspections and tests, conduct a road test to replicate the noise while monitoring the HVAC system's performance. Use the GeekOBD APP to log live data and observe any fluctuations in blower performance and system pressures.
