Compressor HVAC: Testing and Inspection

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 front main bearing or connecting rod, may be caused by loose bolts, nuts, mounting brackets, or a loose A/C clutch assembly.

NOTE: Prior to a vehicle being removed from service or stored for more than two weeks, the A/C compressor should be operated to ensure adequate refrigerant oil distribution throughout the system components. Turn on the A/C for a minimum of five minutes with outside air and the highest blower speed selected.

Drive belts are speed sensitive. At different engine speeds and depending upon belt tension, belts can develop noises that are mistaken for an A/C compressor noise. Improper belt tension can cause a misleading noise when the A/C clutch is engaged, which may not occur when the A/C clutch is disengaged. Check the accessory drive belt condition and tension as described in Cooling before beginning this procedure.
1. Select a quiet area for testing. Duplicate the complaint conditions as much as possible. Switch the A/C compressor on and off several times to clearly identify the compressor noise. Listen to the A/C compressor while the clutch is engaged and disengaged. 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.
2. Loosen all of the compressor mounting hardware and retighten. Tighten the A/C clutch mounting bolt. Be certain that the clutch field coil is mounted securely to the A/C 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 A/C 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 A/C compressor.
6. If the noise is from liquid slugging on the A/C suction line, check the refrigerant oil level and the refrigerant system charge.
7. If the noise continues, replace the A/C compressor and repeat Step 1.