This article discusses an example of an outer race-bearing defect on a 1,250 ton (4400 kW) air-conditioning chiller. The defect was detected using off-the-shelf portable vibration analysis hardware and software. The machine is a single-stage centrifugal compressor with a rolling element thrust bearing on the motor free end and a sleeve bearing on the motor drive end. This article discusses methods used to diagnose and trend the bearing defect using vibration spectra as an indicator of the bearing condition. The diagnostic methods covered are universally applicable to other types of machines (pumps, fans, gears) with rolling contact bearings.