Oil loss is another possible cause of compressor early death. Like a motor vehicle, a refrigeration or air conditioning compressor needs sufficient oil in order to run properly, achieve its design efficiency, and have a longer life.
The most obvious cause is that the system is leaking oil. Telltale signs would be oil on the outside of the system, either in a puddle or possibly in areas where a pipe breach is possible (at joints for example). Examine the system closely for external signs of oil.