When an air compressor refuses to start, the cause is usually electrical, control or protection related rather than a failed airend. Working through the checks in order finds the fault quickly and safely.
Check the basics first
- Power supply, fuses and circuit breaker
- Emergency stop and door switches
- Phase sequence and voltage at the machine
- Controller display for an active fault code
Protection and control faults
Over-temperature, low oil level and high-pressure switches can all block starting. Check that the machine has cooled, the oil level is correct and the pressure switch has reset. A tripped motor overload or phase-loss relay also prevents the contactor from closing.
Motor and starter checks
Verify the contactor pulls in and the motor receives all phases. A humming motor that does not turn points to a failed capacitor, a locked rotor or a mechanical bind. Never repeatedly attempt starts, because a stalled motor draws high current and overheats.