Air Conditioner outside unit not working... Any advice?

My outside air conditioner unit is not working, TRANE XE1000. The breaker keeps tripping. When I reset the breaker and go to the outside unit, I can hear a slight hum. After doing some research online, I thought I would go ahead and change the capassitor and contactors, but it still doesn't work. The fan will spin freely by hand, so I don't think that's the issue. I purchased and installed a booster for the compressor, thinking maybe it was just getting old and having a hard time, but still nothing. I have a blinking green light inside on a circut panel. When I place my power tester on the contactor and capassitor with the power on, I get no reading of power even when the unit is on. Could this be a bad breaker? Any suggestions would be very helpful. Thank you