Compressor HVAC: Testing and Inspection

When investigating an air conditioning 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 operating temperature, and any other special conditions. Noises that develop during air conditioning operation can often be misleading. For example: What sounds like a failed front bearing or connecting rod, may be caused by loose bolts, nuts, mounting brackets, or a loose compressor clutch assembly.

Drive belts are speed sensitive. At different engine speeds and depending upon belt tension, belts can develop noises that are mistaken for a compressor noise. Improper belt tension can cause a misleading noise when the compressor clutch is engaged, which may not occur when the compressor clutch is disengaged. Check the serpentine drive belt condition and tension before beginning this procedure.

1. Select a quiet area for testing. Duplicate the complaint conditions as much as possible. Switch the compressor ON and OFF several times to clearly identify the compressor noise. Listen to the compressor while the clutch is engaged and disengaged. Probe the compressor with an engine stethoscope or a long screwdriver with the handle held to your ear to better localize the source of the noise.

2. Loosen all of the compressor mounting hardware and retighten. Tighten the compressor clutch mounting nut. 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.

3. To duplicate a high-ambient temperature condition (high head pressure), restrict the air flow through the condenser. Install a manifold gauge set to be certain that the discharge pressure does not exceed 2760 kPa (400 psi).

4. Check the refrigerant system plumbing for incorrect routing, rubbing or interference, which can cause unusual noises. Also check the refrigerant lines for kinks or sharp bends that will restrict refrigerant flow, which can cause noises.

5. If the noise is from 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 compressor.

6. If the noise is from liquid slugging on the suction line, replace the accumulator. If the liquid slugging condition continues following accumulator replacement, replace the compressor.

7. If the noise continues, replace the compressor and repeat Step 1.