You press the start button but nothing happens. Most of the time this is either an electrical problem, or the compressor has tripped on a safety device.
What this problem usually means
When a rotary screw compressor won't start at all: no motor hum, no response, the issue is almost always electrical or safety-related. The compressor's control system includes multiple safety interlocks that prevent starting when conditions aren't safe.The good news is that most "won't start" problems are straightforward to diagnose once you know where to look. Work through the electrical chain systematically: power supply, safety circuits, controller, and motor starter.!
Check these first
5–10 minute checks before diving deeper
- Check supply power: is voltage present at the main disconnect?
- Check for errors or fault codes on the controller display
- Verify the emergency stop is pulled OUT (reset position)
- Check and reset the motor overload relay if tripped
- Verify all doors and panels are closed (door safety switches)
- Check for any reset buttons that need to be pressed
- For new installations: verify phase sequence is correct
- Check if the pressure switch is calling for air (tank not already at setpoint)
Common root causes
Why this happens in rotary screw compressors
- No power supply Main breaker tripped, fuse blown, or disconnect switched off. Always check power first: measure voltage at the compressor's main terminals.
- Emergency stop engaged E-stop button pushed in (locked). Must be twisted/pulled to reset. Often overlooked, especially after maintenance or shift changes.
- Motor overload relay tripped Thermal overload protection has tripped due to previous overheating or overcurrent. Reset button is usually on or near the motor starter.
- Safety interlock active Door switches, high temperature lockout, low oil pressure from previous run, or other safety circuits preventing start.
- Phase sequence error (new installs) On new installations or after electrical work, incorrect phase rotation prevents starting. Swap any two phases to correct.
Don't repeatedly press the start button hoping it will eventually work. If the compressor won't start, there's a reason. Repeated attempts can damage motor windings or starter components. Diagnose the root cause first.
Before working on electrical components, ensure power is locked out and tagged out. Capacitors in VFD drives can hold dangerous voltage even after power is disconnected. If you're not qualified for electrical work, call a licensed electrician.
Still stuck?
If the checks above haven't pointed at the cause, post your symptoms in the Q&A. Real-world answers, no sales pitch.