Screw Air Compressor Troubleshooting: 5 Common Problems and Solutions

Screw air compressors are widely used in manufacturing, mining, food processing, automotive production, electronics, chemical processing, and many other industrial applications. They are designed for continuous operation, but improper maintenance, incorrect settings, component wear, and unfavorable operating conditions can still cause performance problems.

Common problems include a compressor that cannot start, low discharge pressure, excessive oil carryover, high discharge temperature, and failure to unload properly.

Understanding the possible causes of these problems can help operators identify faults quickly, reduce unexpected downtime, and maintain stable compressed air production.

1. Screw Air Compressor Cannot Start

When a screw air compressor fails to start, there can be several possible causes. Experienced technicians usually begin with the simplest checks before moving to more complicated electrical or mechanical inspections.

1.1 Electrical Problems

The electrical system should be checked first when the compressor cannot start.

• Incorrect power connections
• Main power switch not properly closed
• Blown fuse
• Insufficient power supply voltage
• Damaged electrical components
• Incorrect pressure or electrical settings
• Faulty start button or control circuit

The supply voltage should be checked against the compressor's rated voltage. Insufficient voltage can prevent the motor from starting normally.

The control panel should also be checked for alarm messages or protection shutdowns.

1.2 Incorrect Operating Conditions

A compressor may also fail to start because of incorrect operating conditions.

• Outlet valve is not in the correct position
• Pressure setting is too high
• Control circuit has not been reset
• Voltage or current protection settings are incorrect
• Emergency stop button has not been released

Modern screw compressors usually include multiple automatic protection functions. If the controller detects abnormal temperature, pressure, current, or other operating conditions, it may prevent the compressor from starting.

Operators should therefore check the controller display for alarm information before attempting repeated restarts.

1.3 Motor or Airend Problems

Mechanical problems can also prevent a screw compressor from starting.

• Motor failure
• Bearing damage
• Airend seizure
• Rotor damage
• Insufficient lubrication
• Blocked oil circuit

Long-term overload operation or insufficient lubrication can cause excessive wear to bearings and rotors.

If the compressor has recently undergone maintenance or airend repair, incorrect installation or improper rotor clearance may also cause startup problems.

Important: Mechanical inspection of the motor or airend should be performed by qualified technicians.

2. Low Discharge Pressure or Reduced Airflow

Low discharge pressure is another common screw compressor problem.

Before inspecting the compressor itself, check whether the plant's compressed air consumption has increased or whether there is significant leakage in the air distribution system.

If air demand has not changed and there are no major leaks, inspect the compressor itself.

2.1 Blocked Air Filter

A dirty or blocked air filter can restrict the amount of air entering the compressor.

This can result in:

• Reduced airflow
• Lower compressor capacity
• Increased pressure drop
• Higher operating costs

Air filters should be inspected and maintained according to the manufacturer's recommended maintenance schedule. Compressors operating in dusty environments may require more frequent inspection.

2.2 Inlet Valve Problem

The inlet valve controls the amount of air entering the compressor. If the inlet valve does not open properly during loading, the compressor may not reach its rated capacity.

Possible causes include:

• Valve contamination
• Mechanical sticking
• Control signal problems
• Worn components
• Damaged actuator

If the compressor has recently been serviced and the filters and oil are in good condition, the inlet valve should be inspected.

2.3 Motor Speed or Drive Problems

A motor that cannot reach the required operating speed may reduce compressor airflow.

Possible causes include:

• Motor winding problems
• Bearing wear
• Shaft problems
• Incorrect electrical supply
• Belt slippage on belt-driven compressors

For belt-driven compressors, belt tension and belt condition should also be inspected.

2.4 Incorrect Pressure Settings

Incorrect pressure settings can create the impression that the compressor has insufficient capacity.

If pressure settings have recently been changed, check the controller parameters and pressure switch.

For industrial applications, pressure settings should be determined according to actual plant requirements and compressor specifications.

3. Excessive Oil Carryover in Compressed Air

Oil carryover occurs when excessive lubricating oil enters the compressed air system. This can be particularly problematic in applications where clean compressed air is important, including food processing, electronics, pharmaceutical production, and certain manufacturing processes.

Common causes include:

1. Excessive oil level
2. Blocked oil return line
3. Damaged oil separator
4. Insufficient system pressure
5. Minimum pressure valve failure
6. Incorrect or poor-quality compressor oil

3.1 Excessive Oil Level

Too much lubricating oil can increase oil carryover. During normal operation, the oil separator separates oil from compressed air. However, if the oil level is excessively high, the separation system may not operate as intended.

Always maintain the oil level within the manufacturer's specified range.

3.2 Blocked Oil Return Line

The oil return system returns separated oil to the compressor airend. If the return line, filter, or orifice becomes blocked, separated oil can accumulate inside the separator.

The excess oil may eventually be carried into the compressed air outlet.

3.3 Damaged Oil Separator

A damaged oil separator can significantly increase oil carryover.

If the separator element is damaged, perforated, or incorrectly installed, oil separation efficiency can decrease dramatically.

The separator should be inspected and replaced according to the manufacturer's maintenance requirements.

3.4 Minimum Pressure Valve Failure

The minimum pressure valve helps maintain sufficient pressure inside the compressor system. If the valve fails, system pressure may become too low for proper oil circulation and separation.

This can result in excessive oil entering the compressed air system.

3.5 Incorrect Lubricating Oil

Compressor oil plays an important role in lubrication, cooling, and oil-air separation.

Using unsuitable oil or mixing incompatible lubricants can cause excessive foaming, poor oil separation, increased oil carryover, and reduced lubrication performance.

Always use lubricant recommended for the specific compressor model and operating environment.

4. High Screw Compressor Discharge Temperature

High discharge temperature is another common screw air compressor problem that should not be ignored. Excessive temperature can affect lubrication, component life, and overall compressor reliability.

Possible causes include:

• Oil stop valve malfunction
• Blocked oil filter
• Thermostatic valve malfunction
• Abnormal oil regulation
• Dirty or blocked oil cooler
• Airend problems
• Blocked air filter
• Oil separator problems
• Faulty temperature sensor
• Controller malfunction

4.1 Insufficient Compressor Oil

Insufficient oil reduces the compressor's ability to lubricate and cool the airend. Check the oil level and inspect the oil circuit for possible leaks or restrictions.

4.2 Poor Oil Condition

Compressor oil gradually deteriorates during operation. High temperature, contamination, moisture, and oxidation can reduce its performance.

Old or degraded oil may have poor heat transfer, increased viscosity, reduced oxidation resistance, and increased foaming.

Regular oil replacement is therefore an important part of screw compressor maintenance.

4.3 Oil Cooler Problems

For oil-cooled systems, a dirty or blocked oil cooler can significantly reduce cooling efficiency.

Check for:

• Dust accumulation
• Blocked cooling passages
• Insufficient cooling airflow
• Water-side fouling on water-cooled systems

Keeping the cooling system clean is essential for maintaining stable operating temperature.

5. Screw Compressor Will Not Unload

Loading and unloading are fundamental functions of a screw air compressor. During normal operation, the compressor should load when compressed air is required and unload when the system reaches the required pressure.

If the compressor cannot unload, pressure may continue increasing until the compressor reaches a protection limit or shuts down.

5.1 Incorrect Pressure Setting

The pressure switch or controller may have an incorrect unloading pressure setting.

Check:

• Load pressure
• Unload pressure
• Maximum pressure
• Minimum pressure
• Controller parameters

5.2 Inlet Valve Failure

If the inlet valve remains open when the compressor should unload, the compressor may continue producing compressed air.

Inspect the valve for sticking, mechanical damage, control problems, or actuator failure.

5.3 Solenoid Valve Failure

The unloading or venting solenoid valve may fail to operate correctly. A faulty solenoid valve can prevent the compressor from entering the correct unloaded state.

5.4 Control Circuit Problems

Electrical or PLC control problems can also prevent unloading.

Check:

• Solenoid valve signals
• Pressure sensor
• Controller
• Wiring
• Control relays

How to Troubleshoot a Screw Air Compressor Efficiently

When troubleshooting an industrial screw compressor, avoid immediately replacing expensive components. A systematic approach is usually more effective.

Step 1: Check the Controller Alarm

• High temperature alarm
• High pressure alarm
• Motor overload
• Oil pressure alarm
• Sensor fault

Step 2: Check Operating Conditions

• Power supply
• Ambient temperature
• Air demand
• Outlet pressure
• Oil level
• Cooling conditions

Step 3: Check Consumable Components

• Air filter
• Oil filter
• Oil separator
• Lubricating oil

Step 4: Check Valves and Control Components

• Inlet valve
• Minimum pressure valve
• Thermostatic valve
• Solenoid valves
• Pressure sensor

Step 5: Check Mechanical Components

If the problem remains, qualified technicians should inspect the motor, bearings, airend, coupling, and drive system.

Preventive Maintenance for Screw Air Compressors

Many screw compressor problems can be reduced through proper preventive maintenance.

A maintenance program should include regular inspection of:

• Air filters
• Oil filters
• Oil separators
• Lubricating oil
• Cooling system
• Belts and couplings
• Valves
• Electrical connections
• Sensors
• Operating pressure
• Discharge temperature

The actual maintenance interval should follow the compressor manufacturer's recommendations and be adjusted according to operating hours and working conditions.

Compressors operating in dusty, humid, or high-temperature environments may require more frequent inspection.

When Should You Contact a Compressor Manufacturer?

Some problems can be solved through routine maintenance, but more serious issues require professional technical support.

Contact a qualified compressor manufacturer or service engineer if you encounter:

• Repeated high-temperature shutdowns
• Motor overload
• Airend seizure
• Abnormal vibration
• Unusual noise
• Persistent oil carryover
• Severe pressure fluctuations
• Repeated controller alarms
• Electrical faults
• Major reduction in compressor capacity

Continuing to operate a compressor with a serious mechanical or electrical fault may cause additional damage and increase repair costs.

Choose the Right Industrial Screw Air Compressor

Selecting the right compressor is just as important as maintaining it properly. Before choosing an industrial screw air compressor, consider the required airflow, working pressure, operating hours, ambient temperature, cooling method, air quality requirements, installation environment, energy efficiency, and maintenance requirements.

For applications with variable air demand, a variable speed drive (VSD) screw compressor can adjust compressor output according to actual demand and may help reduce energy consumption.

For applications requiring high air purity, an oil-free compressor may be more appropriate depending on the required air quality and production process.

Conclusion

Screw air compressors are reliable industrial machines, but proper operation and preventive maintenance are essential for long-term performance.

The five common problems discussed in this guide are:

1. Compressor cannot start
2. Low discharge pressure or airflow
3. Excessive oil carryover
4. High discharge temperature
5. Compressor cannot unload

When troubleshooting, always begin with basic checks such as power supply, operating parameters, filters, oil level, and controller alarms before moving to more complex mechanical inspections.

If the problem involves the motor, airend, electrical system, or major control components, professional technical assistance is recommended.

Need an Industrial Screw Air Compressor?

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