If you or a tech will hang an ammeter on the one of the power wires you will probably see that the compressor is pulling excessive amps when trying to start. Somewhere on the unit you should find a placard that details LRA (locked rotor amps). The compressor will need to be replaced. It won't be a hard jobs for an AC tech. The typical RV tech won't touch it since they normally don't repair ACs. The system will need to be evacuated and refilled with refrigerant after the compressor is replaced. Ask the tech if they will use nitrogen when sweating in the new compressor and if they will install a filter drier. If the answer to either question is no, then look for another tech