Unit just hums & does not compress. Ensure mechanism not jammed by turning gear by hand. Check continuity of centrifugal switch (should be closed with unit off) which is a white plastic sitting at top of motor. If relay is open, simple electrical relay cleaner should restore the contacts.

Greetings all, this issue, which can be fixed with a new motor, is actually a problem with the motor end switch. This switch is used in the start winding circuit for both up and down. If the switch fails in the open position then the motor will not start and it will hum as only the run winding is energized. Removing the top end bell of the motor will expose the end switch and you will see it is burned or black. It can be removed and cleaned, check that it measures closed, about .3 ohms, before you reinstall it. Re check the connection again before testing the compactor. I have not been able to find a replacement end switch as of this posting as I feel that the cost of a motor is a bit much for a bad end switch I will keep looking
Regards Doc'