Owner's Problem Description
The owner of a 2002 Subaru WRX Turbo 4-cylinder reports that after having the A/C system checked and tested, the A/C blows cold air for about 30 seconds before switching to warm air. The system was evacuated and charged successfully without leaks, and the compressor continues to run, but the high-pressure side remains cold. The owner is seeking help to diagnose the issue.
Professional Technical Analysis
The 2002 Subaru WRX features a 2.0L turbocharged engine and an estimated mileage of around 120,000 miles. The A/C system was evaluated, revealing that after initial cooling, the system fails to maintain low temperatures, transitioning to warm air within 30 seconds. The high-pressure side remains cold, indicating potential issues with the expansion valve or refrigerant flow. The reported low-side pressure drops to below 0 psi, suggesting a vacuum state that could indicate blockages or restrictions within the system. The compressor remains operational, which is unusual for a typical failure scenario. Previous work included evacuation and recharging of the system, yet symptoms persist. The high-side pressure reading of 100 psi and the low-side dropping into a vacuum state are concerning as they deviate from standard operational parameters. Under normal conditions, low-side pressures should range from 35 to 40 psi, while high-side pressures should be between 180 and 200 psi at ambient temperatures of around 80°F. Additionally, the compressor operation without adequate refrigerant flow can lead to damage over time. The expansion valve, located within the evaporator unit under the dash, is suspected due to its role in regulating refrigerant flow. Removal of the evaporator will be necessary for direct access to the expansion valve, which is a labor-intensive task requiring careful disassembly of the dashboard area.
Possible Causes
Most common causes (ordered by frequency):
- Expansion Valve Malfunction: The expansion valve may be clogged or stuck, preventing proper refrigerant flow to the evaporator. This could lead to the observed low-side pressure dropping below 0 psi, indicating a blockage. This valve should be replaced if confirmed faulty, as it’s integral to regulating refrigerant flow and ensuring efficient cooling. - Symptoms include fluctuating pressures, inability to maintain low-side pressure, and A/C cooling failure after initial operation.
- Refrigerant Charge Insufficiency: Despite the initial successful recharge, the system may not have enough refrigerant due to leakage or incorrect charging. The required charge for the WRX is between 1.3 to 1.5 lbs. Low refrigerant levels can lead to compressor operation without adequate cooling. - Initial A/C operation followed by warm air suggests insufficient refrigerant flow to the evaporator.
- Compressor Failure: Internal issues within the compressor, such as a failing clutch or internal damage, can prevent it from compressing the refrigerant effectively. If the compressor cannot maintain adequate pressure, it can lead to inefficient cooling and fluctuating A/C performance. - Compressor operation without adequate refrigerant flow can indicate internal issues preventing proper function.
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 Pressure Readings: Begin by taking high and low-side pressure readings with an A/C gauge set to establish baseline operating pressures. For a properly functioning system, the high-side should be between 180-200 psi, while the low-side should be 35-40 psi. If the low-side pressure drops below 0 psi, this indicates a potential blockage.
- STEP 2 - Refrigerant Check: Verify the refrigerant charge in the system to ensure it is within the required range of 1.3 to 1.5 lbs. If the charge is insufficient, recharge the system and monitor pressure readings after the recharge to check for any irregularities.
- STEP 3 - Expansion Valve Inspection: If pressure readings confirm a blockage, inspect the expansion valve for proper operation. Accessing the valve requires removing the evaporator unit, which is a labor-intensive task. Use the appropriate tools to safely disassemble components and check the valve’s functionality.
- STEP 4 - Compressor Functionality Test: If the expansion valve appears functional, conduct a test of the compressor to ensure it is compressing refrigerant effectively. Listen for unusual noises, check for clutch operation, and use a refrigerant management system to confirm refrigerant flow.
