Owner's Problem Description
The owner reports a screeching noise coming from the air conditioning compressor, along with a slipping and screeching belt. This issue has been intermittent over the past few days. An RAA technician inspected the vehicle and confirmed the compressor as the source of the noise. The owner is seeking advice on repair options and cost estimates.
Professional Technical Analysis
The 2005 Mitsubishi Magna, equipped with a 3.5L V6 engine and an approximate mileage of 120,000, presents with a notable screeching noise from the air conditioning compressor. This noise is accompanied by a belt that is slipping, indicating potential wear or misalignment. Given the age and mileage of the vehicle, it is plausible that the serpentine belt has reached its service interval and requires inspection or replacement. The symptom pattern suggests that the noise may originate from the AC compressor clutch or bearing, which is a common failure point in these systems. The intermittent nature of the noise could suggest that the compressor is engaging and disengaging improperly due to insufficient belt tension or a failing clutch mechanism. The vehicle's current condition raises safety concerns, as a failing AC compressor can lead to further damage to the serpentine belt, potentially resulting in a complete failure of engine accessories. It is crucial to conduct a thorough inspection of the AC system, including checking for refrigerant levels, as low refrigerant can also lead to compressor noise. A systematic approach to diagnosing the source of the noise will be essential in determining the exact cause and necessary repairs.
Possible Causes
Most common causes (ordered by frequency):
- Compressor Clutch Failure: The AC compressor clutch may be failing, causing intermittent engagement issues that lead to screeching noises. This is common in vehicles with high mileage where components wear out. A failing clutch can also lead to slipping of the serpentine belt, contributing to the noise. Testing should include checking clutch engagement voltage (typically should receive 12V when engaged) and visual inspection for wear or damage. - Screeching noise when AC engages, visual wear on the clutch surface, potential DTC codes indicating clutch issues.
- Worn Serpentine Belt: The serpentine belt may be worn or damaged, causing slipping during operation and resulting in screeching noises. Normal service life for serpentine belts is around 60,000 miles, and if the belt has not been replaced, it may be time for a new one. A proper inspection should include checking the belt for cracks and measuring tension. - Visible cracks on the belt, slipping during AC operation, tension measured below specifications.
- AC Compressor Bearing Wear: The bearings within the AC compressor may be worn out, leading to noise during operation. This typically occurs in older vehicles or those with high mileage. A worn bearing can cause the compressor to operate inefficiently and create abnormal noises. Inspection of bearing play and noise during manual rotation of the compressor shaft can reveal issues. - Abnormal noises during compressor operation, noticeable play in the compressor shaft, potential performance issues with AC cooling.
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 Visual Inspection: Begin with a thorough visual inspection of the air conditioning compressor, serpentine belt, and associated components. Look for signs of wear, misalignment, or damage. Check if the belt is properly tensioned and inspect the compressor clutch for visible wear or damage. This step is crucial to identify obvious issues before proceeding with further diagnostics.
- STEP 2 - Belt Tension and Condition Check: Use a belt tension gauge to measure the tension of the serpentine belt. It should be within the manufacturer's specifications (usually around 90-100 lbs). Look for any visible signs of cracks or fraying. If the belt tension is low or if there are any signs of wear, replacement of the serpentine belt should be considered.
- STEP 3 - Clutch Engagement Testing: Test the AC compressor clutch by applying 12V directly to the clutch connector. Listen for engagement sounds and check for any abnormal noises. If the clutch does not engage smoothly or produces noise, it may indicate an internal failure.
- STEP 4 - Road Test with AC Functionality: Perform a road test while operating the AC. Monitor for any unusual noises and check the performance of the AC system. Ensure that the compressor engages and disengages properly without any slipping or screeching. Document any issues that arise during this test.
