Tech accessed unit on the roof and found no power to the unit or the disconnect. Tech tested the compressor, blower motor and condenser fan motor. Found no challenge with unit, located breaker panel and found 50 amp breaker labeled entrance A/C in the off position. Tech cut breaker on, went back on roof and verified power at disconnect. Restored power to unit and unit was working at time of departure. Suspect breaker was cut off by mistake.