DIAGNOSIS & TESTING
A/C Compressor 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, transaxle 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 compressor
assembly.
NOTE :
The A/C compressor must be replaced if any unusual noise is heard from the compressor itself.
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 the compressor is operating at maximum displacement, which may not occur when the compressor is at
minimum displacement.
1. Select a quiet area for testing.
2. Duplicate the complaint conditions as much as possible.
3. Turn the A/C system On and Off several times to clearly identify any compressor noise.
4. Listen to the A/C compressor while it is operating at maximum and minimum displacement.
5. 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.
6. To duplicate high-ambient temperature conditions (high head pressure), restrict the air flow through the A/C con-
denser. Install a manifold gauge set or a scan tool to ensure that the discharge pressure does not exceed 2600
kPa.
7. Check the condition of the accessory drive belt.
NOTE: The A/C compressor must be replaced if the drive hub is broken or if the compressor shaft does not
rotate smoothly.
8. Check the compressor hub and pulley and bearing assembly. Ensure that the hub and pulley are properly
aligned and that the pulley bearing is mounted securely to the A/C compressor.
9. 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.
10. Loosen all of the compressor mounting hardware and retighten.
CAUTION: Do NOT run the engine with a vacuum pump in operation or with a vacuum present within the
A/C system. Failure to follow this caution will result in serious A/C compressor damage.
11. If the noise is from the opening and closing of the high pressure relief valve, recover, evacuate and recharge the
refrigerant system. If the high pressure relief valve still does not seat properly, replace the A/C compressor.
12. If the noise is from liquid refrigerant slugging in the A/C suction line, replace the A/C accumulator and check the
refrigerant oil level and the refrigerant system charge.
13. If a slugging condition still exists after replacing the A/C accumulator, then replace the A/C compressor.
Refrigerant System Leaks
WARNING!
R-134a service equipment or the vehicle A/C system should not be pressure tested or leak tested with com-
pressed air. Mixture of air and R-134a can be combustible at elevated pressures. These mixtures are potentially
dangerous and may result in fire or explosion causing property damage, personal injury or death. Avoid breath-
ing A/C refrigerant and lubricant vapor or mist. Exposure may irritate eyes, nose and throat. Use only approved
service equipment meeting SAE requirements to discharge an R-134a system. If accidental system discharge
occurs, ventilate work area before resuming service.
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Chery Automobile Co., Ltd.
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