Owner's Problem Description
The AC compressor in my 2008 Saturn Astra failed in June 2013. I bought an AC Delco compressor and receiver/drier from Rock Auto, which my usual mechanic installed. I also purchased an expansion valve, but it couldn't be replaced due to a mismatch with the original. The system was flushed and the condenser cleaned. However, the AC is still not functioning properly.
Professional Technical Analysis
The 2008 Saturn Astra is equipped with a 2.4L 4-cylinder engine and has approximately 75,000 miles on the odometer. The owner reported that the AC compressor failed back in June 2013, and a replacement AC Delco compressor was installed along with a new receiver/drier. However, an expansion valve was purchased but not replaced due to compatibility issues. The system was flushed, and the condenser cleaned, but the AC system is not functioning as expected. The primary symptom is a lack of cooling, and there are no unusual noises or signs of compressor engagement. Given the history and the fact that the compressor did not engage, further diagnostics are required. The first step should be to check the electrical supply to the compressor’s clutch. This involves applying a direct 12V supply to the clutch connector to see if it engages. If the clutch engages, the compressor may be good, indicating possible issues with the AC control module or pressure switches. If there is no engagement, the compressor may be defective despite being new. Additionally, inspecting the refrigerant levels is crucial, as low refrigerant could prevent the compressor from engaging. It's also worth noting that without a proper replacement of the expansion valve, the system may not operate efficiently. Thorough testing of electrical circuits, including the relay and fuses associated with the AC system, should be prioritized to avoid misdiagnosis.
Possible Causes
Most common causes (ordered by frequency):
- Electrical Supply Issue: The AC compressor clutch relies on a 12V power supply for engagement. If there is no voltage at the clutch connector, the compressor will not engage. This can be due to a blown fuse, faulty relay, or issues in the wiring harness. Checking for continuity and voltage at the compressor's clutch connector is essential. If the system is not receiving proper voltage, it may indicate a problem with the AC control module or related components. - No engagement of the compressor clutch when AC is turned on, testing indicates no voltage at the clutch connector.
- Compressor Failure: Despite being a new unit, the AC compressor may have internal defects or damage during shipping/installation. If the compressor was not tested before installation, it is possible that it was defective out of the box. A direct 12V test to the clutch will help determine if the compressor is functioning. If the clutch engages but the system still does not cool, internal failure could be the cause. - Compressor was replaced but no cooling effect, clutch engagement test indicates potential internal issues.
- Refrigerant Charge Issue: Low refrigerant levels can prevent the compressor from engaging. The AC system should be checked for proper refrigerant levels and any leaks. If the system is low on refrigerant, it could indicate a leak in the system or improper service during the previous repair. Low refrigerant may cause the pressure switches to prevent compressor activation. - AC system not cooling, potential low refrigerant levels causing compressor not to engage.
- Expansion Valve Compatibility: Since the expansion valve was not replaced due to a mismatch, this could potentially affect the overall efficiency of the AC system. An incompatible valve may not properly regulate refrigerant flow, leading to issues with cooling performance. It is crucial to verify that the expansion valve is suitable for the system to ensure optimal operation. - Mismatch in expansion valve could lead to inefficient cooling, affecting overall AC performance.
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 - Electrical Verification: Start with a thorough inspection of the AC compressor electrical circuit. Use a multimeter to check for 12V at the compressor's clutch connector when the AC is activated. If there is no voltage, trace the wiring back to the AC control module and inspect the relay and fuses for continuity. This step is crucial to ensure proper operation of the compressor.
- STEP 2 - Compressor Clutch Test: If voltage is present at the clutch connector, proceed to test the compressor clutch engagement. Apply 12V directly to the clutch connector to see if it engages. Listen for any sounds indicating internal movement. If the clutch engages, the compressor may still have internal issues; if it does not, the compressor might be defective.
- STEP 3 - Refrigerant Level Check: Check the refrigerant charge in the system using a set of manifold gauges. Verify that the system is properly charged to the manufacturer specifications (typically around 30-40 PSI on the low side when the system is off). If the levels are low, inspect for leaks using a UV dye or electronic leak detector. Address any leaks before recharging the system.
- STEP 4 - System Performance Evaluation: After addressing identified issues, run the AC system and monitor performance. Check the temperature at the AC vents to see if it meets the expected output (typically 40-50°F). If performance is still inadequate, further diagnostics may be necessary to explore issues within the expansion valve or AC control module.
