ac unit keeps tripping breaker

Great news: yup it was a loose micro board in the junction box. It actually was arcing to the box. Black wire. Easy fix and thanks so much for the replys that probably saved me huge $$ if I were to take it into a shop.

Fan runs no problem. Only when cool is turned on and its immediately tripped. It makes a makes a quick buzzing sound at the breaker then "pop"

If it trips the breaker the instant you call for cooling, it almost has to be either a short in the wiring, a shorted capacitor, or a bad compressor.
If it runs for a bit, look at the condenser (outside) coils and the fan blades.

Many years ago I had the same issue with a new travel trailer. I don't remember how many times or places I had used the air conditioning without issues before hooking up to one park's power only to blow the park's post circuit breaker immediately. Got the park ranger to come out assuming there was something wrong with the park power, since I had a new trailer and figured my trailer couldn't have been the problem. Naturally the park power was fine and they actually had a GFCI wired into the pedestal. After turning off different circuit breakers in the trailer we narrowed it down to being the air conditioner that was causing the problem. When we got home and took the inside housing down we discovered one wire had a bare spot that was grounding out on the metal frame of the electrical box in the unit. It had been wired that way when they installed the AC at the factory.

Start capacitors.....fan and compressor. Especially compressor.
Bulging/leaking

Does fan run.....t-stat fan ON ?

Compressor motor could be bad