5 Common Problems in Oil-Free Screw Air Compressors and How to Fix Them

Oil-free screw air compressors are essential in industries where clean, oil-free compressed air is critical—such as food, pharmaceuticals, electronics, and medical facilities. However, even with their advanced design and minimal oil content, these machines can still encounter a variety of performance issues over time.

In this guide, we’ll cover the top 5 common problems in oil-free screw air compressors, what causes them, and how to troubleshoot them efficiently.

1.  Compressor Fails to Start

If your oil-free screw compressor won’t start, it can often be traced back to one of several simple issues:

• Blown fuse: One of the most frequent culprits.

• Faulty overload relay: The protective relay may have failed, disabling the system.

• Start button malfunction: Poor contact is rare but can happen with older or lower-quality machines.

• Low supply voltage: Inadequate input voltage can prevent the motor from running.

• Motor failure: A more serious issue that usually requires inspection by the manufacturer or service team.

Pro tip: Always check the fuse and voltage first before moving on to more complex diagnostics.

2. Low Exhaust Pressure

When the compressor is running but the output pressure is too low, consider these four possible causes:

1. Faulty intake valve – May not open or close properly.

2. Excessive air demand – The system may be undersized for your application.

3. Clogged air filter – Dirt or debris in the air filter restricts airflow.

4. Blocked oil-air separator element – A dirty separator core reduces efficiency.

Note: These issues are more common in units that have been in use for several years.

3. Excess Oil in Compressed Air

One of the key benefits of an oil-free compressor is clean air. But if oil appears in the output, here are six likely causes:

• Oil level too high: Overfilled oil can cause carryover.

• Blocked return oil pipe or throttle orifice: Prevents proper oil recirculation.

• Damaged oil separator element: Allows oil mist to pass into the air stream.

• Oil regulation system leakage: Leaks may result in oil mixing with the air.

• Low working pressure: Causes poor oil separation.

• Poor oil quality or excessive foaming: Substandard or unsuitable lubricants can lead to misting.

Solution: Regularly inspect and replace oil separator elements and always use approved lubricants.

4. High Discharge Temperature

When the discharge temperature exceeds 150°C (302°F), the compressor may enter a fault state or shut down to prevent damage.

Possible reasons:

• High ambient temperature: Poor ventilation increases internal temps.

• Temperature control valve failure: Prevents proper oil flow and cooling.

• Dirty oil cooler: Reduces heat dissipation efficiency.

• Blocked oil filter: Restricts flow and causes overheating.

• Faulty fan or thermal resistor: Cooling system cannot operate properly.

Tip: Clean the cooler regularly and monitor ambient temperatures in the compressor room.

5. Compressor Cannot Unload (No Load Condition Not Triggered)

If your compressor stays loaded and cannot unload properly, it may be due to:

• Faulty intake valve actuator: Prevents the valve from closing during unloading.

• Malfunctioning pressure sensor: Fails to signal unloading conditions to the controller.

Much like automobiles, oil-free screw compressors require regular and proper maintenance to prevent these issues and ensure long-term reliability. Skipping routine inspections or using the wrong methods can lead to frequent breakdowns and costly repairs.

Final Thoughts

By understanding these common problems in oil-free screw compressors, operators and maintenance teams can proactively prevent failures, reduce downtime, and extend equipment lifespan.

Remember: Preventive maintenance is not optional—it’s essential. Follow the manufacturer’s guidelines, use OEM parts, and monitor your system performance closely.

Air compressor maintenance issues