To quote the Sanden Manual:
"10.5 Unusual Noise Not due to Compressor
Unusual noises may be caused by components other than the compressor.
1. Compressor Mounting - Check for:
· Loose belt - see belt tension specifications.
· Broken bracket or compressor mounting ear. Replace broken component.
· Missing, broken, or loose mounting bolts. Replace, reinstall, or tighten.
· Flush fit of compressor to bracket and vehicle engine. Replace any part not properly fitted.
· Loose or wobbling crankshaft pulley. Check for damage to pulley, incorrect center bolt torque or
center bolt bottoming. Repair to vehicle manufacturer's specifications.
· Bad idler pulley bearing. Replace if necessary.
2. Other Engine components - Check for noise in:
· Alternator bearing
· Air pump (if present)
· Water pump bearing
· Timing belt or chain
· Power steering pump (if present)
· Loose engine mount bolts.
10.6 Unusual Noises Due to Compressor
1. Suction pressure less than about 5 psig can cause unusual noise. Charge refrigerant to proper
amount and test by applying heat to evaporator to increase suction pressure.
2. Clutch bearing--See clutch Inspection in section 10.4
3. Oil level--insufficient oil can cause unusual noise. See Oil Level Check Procedure in Section 10.2.
4. Valve Noise--test for valve plate assembly failure per Valve Plate Test Procedure in Section 10.7."