One of the more elusive causes of three-phase compressor motor overheating and failure is an imbalance in voltage.
Compressor voltage unbalance can be found with a voltmeter by measuring between phases on the compressor’s motor terminals, at the compressor’s disconnect, or at the compressor’s contactor or starter terminals. Some of the more common configurations in three-phase motor windings are the Wye and Delta configurations (See Figure 1).