1- Turn off the power and check the fuse and electrical connections.
2- Test the power to the "motor only" by removing the belt.
a) Unplug pump motor from power source.
b) Taking care not to pinch fingers, belt can be removed similar to a bicycle chain removal procedure.
c) Plug into power source.
d) Taking care to avoid potentially spinning motor pulley, turn motor power to the on position.
e) If motor pulley spins, the motor is good and the vacuum pump is seized.
3- Try manually turning pump - With belt removed, as in 2 above, try hand-rotating the pump pulley clockwise with the pump intake port open. If pump will not turn, sometimes rocking the pulley back and forth (clockwise, counter -clockwise) will free the pump. If the pump will not turn by hand, using only hand strength, do not use leveraging or power tools to turn the pump pulley, because vital, expensive pump parts may be damaged. It is best at this point to professionally service the pump.
4- If motor pulley does not spin - Compare the pump motor rating, printed on a label on the side of the motor and on the serial number tag, to the power source, to be sure they agree in voltage, phase, and frequency. If power source is correct and motor pulley will not spin, the motor needs replacing.
If both motor and pump turn freely then replace the belt and check the belt tension. The tension should be sufficient to drive the pump without visible slippage. Any greater tension will cause noise and possible damage to the bearings of both the motor and pump. Make certain that both pulley grooves are clean and free from oil. The pulleys must be fastened securely on their respective shafts, and in parallel alignment. Use a straight edge to inspect belt alignment.