Over the past month we have replaced 3 compressors on the same Trane rooftop unit. The 20-ton unit has two compressors and the same compressor has blown three times in a row. Since the unit is 20 years old initially the compressor was thought to have died from natural causes. But when the second one was blown our technicians proclaimed that there was an electrical problem, because the contractor had locked out. Con Edison was brought in to inspect if there had been any spikes, they found nothing wrong. After we noticed that the unit had tripped we called our HVAC service to let them know that then 3-day-old compressor may have just died again. Much to my dismay we found that the new compressor had blow. A recent theory from our technician is the electrical problem is from the phase monitor. Is it possible that the phase monitor has been the source of the problem?