Common Screw Air Compressor Inverter Faults: A Practical Guide from Symptoms to Solutions

In industrial environments, the screw air compressor is one of the most critical pieces of equipment for maintaining production efficiency. At the heart of its operation lies the inverter (frequency converter)—the “power regulation center” responsible for adjusting motor speed and ensuring stable performance. However, when the inverter fails, it can cause costly downtime and disrupt the entire production line.

This practical guide explains the five most common screw air compressor inverter faults, their symptoms, causes, and proven solutions—helping you diagnose issues faster, minimize downtime, and extend the service life of your equipment.

1. Overload Fault: A Warning Sign of Power Overload

Symptoms:

• The inverter panel displays the “OL” (Over Load) error code.
• The compressor struggles to accelerate or shuts down automatically.

Main Causes:

1. Excessive mechanical load — such as worn bearings or rotor jamming in the compressor head, increasing resistance and current.
2. Incorrect inverter settings — a too-short “acceleration time” parameter causes a high startup current spike.
3. Aging hardware — degraded current detection circuits may falsely trigger overload protection.

Troubleshooting Steps:

• Inspect mechanical components first: Stop the compressor and manually rotate the rotor. If it jams or makes abnormal noises, repair bearings or clean deposits.
• Adjust inverter settings: Increase acceleration time from 5–10s to 15–20s depending on motor power.
• Check internal components: Use a multimeter to verify the current sensor’s accuracy; replace if deviation exceeds 10%.

2. Overvoltage Fault: When Voltage Surges Beyond Safe Limits

Symptoms:

• “OU” (Over Voltage) code appears on the inverter panel.
• The inverter contactor may trip during shutdown or deceleration.

Core Causes:

• Power grid fluctuations caused by nearby high-power equipment like welders or pumps.
• Faulty braking circuit, preventing regenerative energy from dissipating and causing a DC bus voltage rise (usually above 700V).

Solutions:

1. Measure and stabilize input voltage: If voltage varies more than ±10%, install an AC voltage regulator or input reactor.
2. Test the braking resistor: If resistance is infinite, replace it with the same specification (typically 10Ω–50Ω).
3. Inspect the braking unit’s IGBT module: Replace any damaged components and recalibrate braking parameters.

3. Undervoltage Fault: The Root Cause of Insufficient Power

Symptoms:

• The inverter displays “LU” (Low Voltage).
• The compressor fails to start or suddenly stops.

Typical Causes:

• Low grid voltage, especially during peak usage or due to undersized/long power cables.
• Faulty rectifier bridge in the inverter, preventing proper AC-to-DC conversion.
• Poor electrical connections at switches or contactors.

Troubleshooting:

• Check input voltage under load: If below 360V (for 380V mains), coordinate with the power supplier or use thicker cables (e.g., 16mm²).
• Test the rectifier bridge: In diode mode, infinite or zero resistance indicates damage. Replace the module if necessary.
• Clean and secure electrical contacts to prevent voltage drops.

4. Overheating Fault: Emergency Alert of Excessive Temperature

Symptoms:

• The inverter shows “OH” (Over Heat).
• Cooling fan stops or slows down.

Common Causes:

1. Faulty cooling fan due to motor failure or bearing issues.
2. Dust and oil buildup blocking heat sinks and reducing airflow.
3. High ambient temperature above 40°C, especially in enclosed workshops.

Fix & Prevention:

• Replace faulty cooling fans with matching models.
• Clean heat sinks using compressed air (≤0.5MPa) carefully to avoid damage.
• Improve workshop ventilation or install localized cooling for the inverter.

5. No Output Fault: When the Inverter Fails to Drive the Motor

Symptoms:

• Inverter powers on, but the motor does not run.
• No response after pressing the start button.

Probable Causes:

• Faulty control signal wiring or incorrect parameter settings (e.g., run command source not set to “external control”).
• Burnt inverter IGBT module preventing AC output.
• Motor winding failure or grounding issue causing automatic inverter shutdown.

Troubleshooting Process:

• Verify control cable integrity and parameter configuration.
• Measure motor winding resistance; replace or repair if readings are zero/infinite.
• Check and replace IGBT power modules if defective, then recalibrate inverter settings.

Proactive Maintenance: The Key to Reliable Operation

The best way to avoid inverter faults is through preventive maintenance.
Perform a monthly inspection that includes:

• Cleaning dust from the inverter’s cooling fins.
• Checking fan operation and air flow.
• Measuring mains voltage and recording key inverter parameters (current, voltage, temperature).

By understanding these five common inverter faults—overload, overvoltage, undervoltage, overheating, and no output—you can quickly identify problems, reduce downtime, and keep your screw air compressor running efficiently.

If you encounter a complex fault, do not disassemble the inverter blindly. Always refer to the equipment manual or consult a qualified technician to prevent further damage and ensure safety.