A/C System Noise Testing

A/C SYSTEM NOISE TESTING

When investigating an A/C system related noise, you must first know the conditions under which the noise occurs. These conditions include: weather, vehicle speed, transmission in gear or neutral, engine speed, engine temperature and any other special conditions. Noises that develop during A/C operation can often be misleading. For example: what sounds like a failed bearing, may be caused by loose bolts, nuts, mounting brackets or a loose A/C compressor.

NOTE: The A/C compressor must be replaced if any unusual noise is heard from the compressor itself.

1. Select a quiet area for testing. Duplicate the complaint conditions as much as possible. Turn the A/C system On and Off several times to clearly identify any compressor noise. On variable displacement compressors, listen to the A/C compressor while it is operating at maximum and minimum displacement. On fixed displacement compressors, listen to the compressor while the A/C clutch cycles on and off. Probe the A/C compressor with an engine stethoscope or a long screwdriver with the handle held to your ear to better localize the source of the noise. To duplicate high-ambient temperature conditions (high head pressure), restrict the air flow through the A/C condenser. Install a manifold gauge set or a scan tool to be certain that the discharge pressure does not exceed 2600 kPa (377 psi).

NOTE: Drive belts are speed sensitive. At different engine speeds and depending upon drive belt tension, drive belts can develop noises that are mistaken for an A/C compressor noise. Improper drive belt tension can cause a misleading noise when a variable displacement A/C compressor is operating at maximum displacement, which may not occur when the compressor is at minimum displacement, or when a fixed displacement compressor clutch is engaged.

2. Check the condition of the accessory drive belt Testing and Inspection.

NOTE: On variable displacement A/C compressors, the compressor must be replaced if the drive hub is broken or if the compressor shaft does not rotate smoothly.

3. When equipped with a variable displacement A/C compressor, check the compressor hub and pulley and bearing assembly. Be certain that the hub and pulley are properly aligned and that the pulley bearing is mounted securely to the A/C compressor Service and Repair.
4. When equipped with a fixed displacement A/C compressor, check the compressor clutch retainer. Be certain that the clutch coil is mounted securely to the compressor, and that the clutch plate and pulley are properly aligned and have the correct air gap A/C Compressor - Installation.

NOTE: The A/C compressor must be replaced if any debris or unusually discolored oil is found on the A/C compressor manifold.

5. Check the refrigerant system plumbing for incorrect routing, rubbing or interference, which can cause unusual noises. Also check the refrigerant lines and hoses for kinks or sharp bends that will restrict refrigerant flow, which can cause noises.
6. Loosen all of the compressor mounting hardware and retighten A/C Compressor - Removal.

CAUTION: Do NOT run the engine with a vacuum pump in operation or with a vacuum present within the A/C system when equipped with the Denso 6SEU16 variable displacement compressor. Failure to follow this caution will result in serious A/C compressor damage.

7. If the noise is from opening and closing of the high pressure relief valve, recover, evacuate and recharge the refrigerant system Refrigerant System Charge. If the high pressure relief valve still does not seat properly, replace the A/C compressor A/C Compressor - Removal.
8. If the noise is from liquid refrigerant slugging in the A/C suction line, check the refrigerant system charge Refrigerant System Charge. If the refrigerant charge is ok, replace the A/C receiver/drier A/C Receiver Drier - Removal and check the refrigerant oil level Refrigerant Oil Level.
9. If a slugging condition still exists after replacing the A/C receiver/drier, then replace the A/C compressor A/C Compressor - Removal.