Get a good voltage meter and check two things. One, that all three lines are hot. Second, check the actual voltage on each line. Just because you are supposed to have say 220 volts service, it may be much lower. If they check out OK, make sure you are on the proper tap terminals for your voltage.
P.S.: Also make sure the previous owner did not have it set up with the high voltage option---440 volts I believe. They could have been running 440 three phase.