Thanks for looking at my profile. I hope I can be of service.
In those cases its usually a very stuck or partially grounded compressor... a completely shorted to compressor will trip the breaker instantly.
If you have an ohm meter and are good with it... do this:
Kill the power to the unit, verify its OFF, then pull the three wires off of the compressor, mark them C, S. R same as on the compressor... this is important.
then use the ohm meter to check resistance to ground...if you get no resistance to ground from any of those that compressor is toast.
then pull a cap off of the refrigerant charging port, depress the schraeder valve core and sniff the gas that comes out...if its acidic/ burnt smelling you are in trouble...time to buy a whole new unit and have it installed to get rid of any contaminants.
If it sniffs clean, the compressor can be replaced....but I don't recommend it if the unit is over 5 years old... the new ones are better, cheaper and the utility company will often pay half of the cost of upgrading it.
I hope that helps,