When a rotary screw compressor runs but won't load (build pressure), the inlet valve isn't opening to allow air into the compressor. The compressor spins, you can hear it running, but tank pressure stays low or doesn't rise at all.
In about 70% of cases, this is a control air supply chain problem—the solenoid valve, electrical signal, or control air lines. The remaining cases involve the inlet valve itself or loss of control air pressure.
Rotary Screw Troubleshooting
Compressor Won't Load – Rotary Screw Air Compressor Troubleshooting
Compressor runs but won't build pressure—the inlet valve isn't opening. Usually a control air or solenoid valve problem.
Industrial systems
Field-tested diagnostics
Independent & unbiased
Safety Notice
Before working on control air lines or the inlet valve, ensure the compressor is off, depressurized, and locked out. Control air is at system pressure (7-10 bar) and can cause injury.
What this problem usually means
Check these first
5–10 minute checks before diving deeper
- Is the compressor in LOAD mode on the controller? (check display/indicator)
- Listen for the solenoid valve click when loading/unloading
- Check for control air at the inlet valve actuator—disconnect the line and feel for air
- Verify no safety interlocks are active (E-stop, high temp, low oil pressure)
- Check solenoid valve electrical connection—is it plugged in securely?
- Look for fault codes or alarms on the controller display
- Verify control air supply line from separator to solenoid isn't kinked or disconnected
- Check if inlet valve moves freely when actuated manually (with compressor off and depressurized)
Common root causes
Why this happens in rotary screw compressors
Solenoid valve failure
Most common cause (60% of cases). Solenoid can be stuck mechanically from dirt/sludge, have a burned coil, or be the wrong voltage.
No electrical signal to solenoid
Controller not sending load signal, safety interlock active, wiring fault, or blown fuse in solenoid circuit.
Control air line blocked
Line between solenoid and inlet valve is kinked, plugged with dirt/moisture, or disconnected.
No control air supply available
MPV (minimum pressure valve) leaking or bypass hole plugged—compressor can't build the initial pressure needed for control air.
Inlet valve stuck or damaged
Inlet valve actuator failed, diaphragm torn, linkage broken, or valve stuck in closed position.
What NOT to do
Don't replace the solenoid valve without testing it first. Check: Does it click? Does air pass through when energized? New parts can be defective or wrong voltage. Verify the existing part is actually faulty before ordering a replacement.
Full Rotary Screw Troubleshooting Manual
Step-by-step diagnostics, root cause logic, and practical fixes for oil-injected rotary screw compressors. Save time and reduce downtime with proven methods.
- Step-by-step diagnostics for common failures
- Root cause analysis techniques
- Practical fixes with parts notes
- Works across all major brands