I have burned out two compressor motors in a very short period of time and want to know if anyone has any ideas on what to check, I would greatly appreciate the help.

The compressor motor is a Leeson Air Compressor Electric Motor — 5SPL HP, Model# 116845.  I replaced the motor about 3 weeks ago and it the second motor to go out withing a short time period.  I have checked my connections and everything appears to be up to par.  

I have tested the wall receptacle and it is putting out approximately 120v per side of a single phase outlet.  I have also tested the power to both sides of the switch and at the motor to ensure it is receiving power.  The compressor pump also spins normally, so I do not think it is overworking the motor. 

I mentioned that I checked approximately 120v on each side of the plug, combines for about 240.  The voltage at the motor is also about 240v.

The unloader valve is working as it is supposed to.  The compressor is cutting out at it's pre set 120psi as advertised. 

Explaining where I think some of the above questions are leading...

Just because you read the correct voltage at the receptacle when nothing is plugged into it and running, doesn't mean you have enough power available at that receptacle. A very common occurrence is that the load is too heavy for the size of wire you have running to the receptacle and it is causing a voltage drop as soon as the current starts to be drawn by the compressor. That motor draws 15A at 230V when fully loaded. If you have 14ga wire running to your receptacle, that may be fine as long as the run length is short and there is nothing else running on that wire at the same time. But if it is part of another circuit with other loads, and/or the distance is over a few yards, voltage drop may be causing your motors to burn up. Even with heavier gauge wire, the starting current may be so high that it causes an immediate voltage drop and the motor is never getting to full speed, so it ends up running on the starting capacitors the entire time, which would also affect a premature death.

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