Why Does My Air Compressor Keep Shutting Off?

If a compressor keeps tripping, it isn’t random. 

Something in the system is wrong, and the controls are stepping in to protect it.

That kind of interruption has a knock-on effect. Production plans slip. Output drops. 

For UK businesses, compressor trips are a common cause of unplanned downtime, with the cost often quoted at around £335 per minute.

Resetting it and carrying on can feel like the fastest option. But if you haven’t found what caused the trip, you’re usually setting yourself up for a worse failure later.

Take the time to investigate properly before you restart it. 

This post tells you how to fix scroll compressors and rotary screw compressors. The main focus is on the electrical, mechanical, and thermal systems that are found in Atlas Copco and other industrial buildings.

This guide will help you diagnose and fix common causes of air compressor shutdowns, focusing on electrical, mechanical, and thermal issues in both scroll and rotary screw models. We’ll also touch on piston compressors, another common type of air compressor.

What Causes Air Compressor Overheating and Shutting Off?

If your air compressor is overheating and shutting off, it’s likely due to one of several common issues. These range from simple problems like a dirty air filter to more complex issues within the cooling system or electrical components. Understanding these potential causes is the first step in diagnosing and resolving the problem.

Safety and Compliance: The First Priority

Before any testing starts, stop and think about safety first.

Industrial compressors don’t just switch off and become harmless. Pressure can stay trapped in the system, and high-voltage electrical supplies are still present. 

Handled incorrectly, either can lead to serious injury. That’s why proper isolation is essential, and why all work should be carried out in line with UK safety regulations before any investigation or repair starts.

• Pressure Systems Safety Regulations 2000: Any work involving pressure relief valves or pressure boundaries requires a competent person.
• Electricity at Work Regulations 1989: Live testing should only be performed if strictly necessary and safe to do so.
• Lock Out Tag Out: Always isolate the main supply. Modern compressors with “Auto Restart” logic may appear off but can start unexpectedly.

Why Is My Compressor Overheating? (Thermal Shutdowns)

Overheating is a very common cause of compressor shutdowns. If the heat generated during compression cannot be released, the temperature rises. Eventually, it reaches the safety limit (typically 110°C to 120°C for Atlas Copco GA series) and the machine stops.

Cooler Fouling and the “Wool Blanket” Effect

A quick look at the outer cooler face might suggest it is clean. However, in many industrial environments, the cooling fan pulls in airborne dust. This dust can build up on the leading edge of the cooler matrix.

A layer of dust often forms between the cores on machines with stacked coolers. This dust acts like a “wool blanket.” 

If a quick wipe across the cooler leaves dust on your finger, airflow inside the unit is likely being choked. Once that happens, the dryer often can’t pull the air temperature down far enough to do its job.

• Cleaning Note: This is usually done by blowing compressed air back through the machine. Angle matters here. Get it wrong and the aluminium fins can bend, which only makes the airflow problem worse.

Thermal Bypass Valve Issues

The thermal bypass valve manages oil temperature. On start-up, the compressor routes oil around the cooler to help it warm up quickly. As the temperature rises, the valve is meant to open and divert the oil through the cooler. 

If it sticks in the cold position, that diversion never happens, and the oil continues circulating without any cooling. It just keeps circulating as temperatures climb. And temperatures rise fast. 

In most cases, the machine will shut down within minutes to protect itself. 

Ventilation and Airflow

If a compressor trips on hot days, the ventilation in the plant room may not be good enough. The machine needs a constant flow of fresh air and can’t use its own hot exhaust air again. Engineers use a certain formula to figure out the needed ventilation airflow (Qᵥ):

Qv = Qheat / (1.2 × 1.005 × ΔT)

A typical 75 kW compressor needs a large volume of airflow to stay within a safe temperature range, usually somewhere between 20,000 and 22,000 m³/h.

It’s also worth checking the intake louvres. If they’re partially blocked or poorly positioned, even a correctly sized ventilation setup can fall short.

Air Intake Restriction

Anything that limits airflow on the inlet side causes problems. A dirty air filter. Ducting that’s too small, too long, or badly routed.

With restricted airflow, the compressor ends up straining to pull air in. Heat builds as a result. Keep running like that and sooner or later the temperature limit is reached and the machine shuts itself down.

Is It an Electrical Supply or Motor Issue?

If the cooling side checks out, turn your attention to the power supply next. Electrical trips usually happen immediately upon startup or when the motor shifts modes.

Voltage Imbalance

Compressors are sensitive to power quality. A small imbalance in the voltage supply (even 2%) can cause a much larger imbalance in the current. This makes the motor windings hotter than normal.

It is also worth checking the phase rotation. If the phases are reversed, the cooling fan may spin backwards. This reduces cooling efficiency and can cause faults during startup.

Star-Delta Transition Trips

Some units trip specifically when switching from “Star” (startup) to “Delta” (run) mode. This often points to a mechanical load issue, such as the compressor trying to build pressure too early or worn electrical contactors.

Overload Relay vs. Thermistor

The specific error can help identify the problem:

• Overload Relay Trip: This measures current (Amps). It usually means the motor is working too hard due to mechanical drag or power issues.
• Thermistor Trip: This measures heat in the windings. It often suggests the motor cooling fan is blocked or the ambient temperature is too high.

Mechanical Failures and Control Loop Issues

If the electrical systems are stable, the issue may lie within the mechanical components or oil circuit.

Minimum Pressure Valve (MPV)

The MPV maintains internal pressure to ensure oil circulates correctly. 

If it sticks open at startup, the system cannot build enough pressure to push oil into the rotors. Without sufficient oil flow, the temperature can rise rapidly, leading to a trip within 30–90 seconds.

Separator Element Blockage

The oil separator removes oil from the air. Over time, it can become clogged. If the pressure difference across the separator becomes too high (typically over 0.7–1.0 bar), the motor has to work much harder to push air through. This increased load can trigger an overload trip.

Blocked Scavenge Line

The scavenge line recovers oil from the separator. 

If this line becomes blocked, oil is pushed downstream into the air pipes. This lowers the oil level in the system, causing it to run hotter. Regular compressed air leak detection surveys can often spot this issue by identifying oil in the distribution piping.

Bearing Wear

Wear in the compressor bearings can increase friction. This puts extra load on the motor, drawing more power until the safety relay activates.

Troubleshooting Atlas Copco Fault Codes

If your Atlas Copco compressor is running an Elektronikon controller, it tends to speak up when there’s a problem. The unit will throw a fault code on the display, which points you in the right direction straight away.

That code is often the quickest way to narrow down the cause and understand why the unit has stopped.

• F21 (Motor Overload): The thermal relay is now on. This suggests high current draw or a power supply issue.
• F52 (Element Outlet Temperature): The unit is running too hot. Check cooling air, oil levels, and cooler cleanliness.
• F34 (Fan Motor Overcurrent): The circuit for the fan motor has tripped. This happens a lot in places with a lot of dust, where the fan blades get heavy with dirt.
• F5 (Low Oil Level): The system has found that there isn’t enough oil. Look for leaks or carryover.

Preventing Future Shutdowns: A Maintenance Strategy

Unplanned shutdowns are rarely sudden. In most cases, they’re the result of a number of small issues, things that were allowed to build up over time.

Regular maintenance interrupts that pattern. Inspect the compressor properly, and catch wear early. Change parts before they fail and breakdowns become far less likely.

Simple Daily and Weekly Checks

• Daily: Check oil levels in the sight glass. Drain condensate to keep the system dry.
• Weekly: Inspect the cooler. Wipe the surface to check for dust. Ensure the room ventilation is clear.

Planned Preventative Maintenance

• Quarterly: Oil sampling can reveal internal wear. High iron content suggests gear wear, while other markers can indicate cooler issues.
• Annual: Replace filters and test safety devices.
• Audit: Review your system setup. Correct sizing saves energy & money and prevents the stress caused by a compressor that is starting and stopping too frequently.

Frequently Asked Questions

Why does my air compressor shut off after a few minutes?

In most cases, it comes down to heat. If the cooler is blocked, or the thermal valve isn’t doing its job, that heat has nowhere to go.

With nowhere for the heat to escape, temperatures rise fast. It doesn’t take long, often just five to ten minutes, before the safety limit is reached and the compressor shuts down to protect itself.

Why does my compressor trip the circuit breaker immediately?

Immediate trips often suggest an electrical short, a mechanical blockage, or a fault during the startup sequence. It is best not to reset the breaker repeatedly.

Should I reset a compressor that keeps tripping?

It is better to investigate first. A trip is a safety mechanism protecting the machine. Resetting without finding the cause could lead to more significant damage.

Why does my compressor get hot so quickly?

If temperatures climb in under 90 seconds, the problem is often oil flow. When oil isn’t circulating as it should, heat builds almost immediately.

In many cases, the issue comes back to a valve that isn’t moving as it should. Once oil flow is restricted, the rotors are left without cooling or lubrication. Heat then builds extremely fast. 

How Can I Tell if My Air Compressor is Overheating?

The most common signs of an overheating air compressor include the unit shutting down unexpectedly, a burning smell, and unusually high temperatures on the compressor’s surface. 

You might also notice that the compressor is running louder than usual or that the cooling fan is working overtime. Regular checks of the operating temperature can help you identify potential issues early on.

What is the normal operating temperature for a screw compressor?

The normal operating temperature for a screw compressor typically ranges between 80°C and 100°C (176°F and 212°F). However, this can vary depending on the specific model and operating conditions. It’s important to consult the manufacturer’s guidelines for your specific compressor to ensure it’s running within the recommended temperature range. Exceeding this range can lead to overheating and potential damage.

Can I bypass the pressure switch to keep running?

No, bypassing the pressure switch is not recommended. The pressure switch is a critical safety device that protects the air compressor from over-pressurisation. Bypassing it can lead to dangerous situations, including equipment damage or even explosions. 

If you’re experiencing issues with your pressure switch, it’s best to consult a qualified technician to diagnose and repair the problem.

What Does a Burning Smell Mean?

A burning smell coming from your air compressor is a serious warning sign that something is wrong. It could indicate overheating components, worn belts, or electrical issues. 

Immediately shut down the compressor and investigate the source of the smell. Continuing to run the compressor with a burning smell can lead to further damage and potential safety hazards.

Trip vs. Shutdown: What Is the Difference?

While the terms “trip” and “shutdown” are often used interchangeably, they can have slightly different meanings in the context of air compressors. A “trip” typically refers to an immediate interruption of power due to a safety mechanism, such as an overload relay or a high-temperature sensor. 

A “shutdown,” on the other hand, may be a more controlled process, initiated by the compressor’s controller in response to a fault or abnormal condition. In both cases, it’s important to investigate the underlying cause to prevent future issues.

What About Air Leaks?

Air leaks can cause your air compressor to work harder, leading to overheating and potential shutdowns. Even small leaks can significantly impact the compressor’s efficiency and lifespan. 

Regularly inspect your air lines, fittings, and connections for leaks. You can use a soapy water solution to identify leaks; bubbles will form where air is escaping. Addressing air leaks promptly can prevent more serious problems down the road.

What About Pressure Switch Problems?

A faulty pressure switch can also cause your air compressor to shut down unexpectedly or cycle on and off too frequently. The pressure switch controls the motor, turning it on when the pressure drops below a certain level and turning it off when the pressure reaches the desired level. 

If the pressure switch is malfunctioning, it may not accurately sense the pressure, leading to erratic behaviour. Testing and replacing a faulty pressure switch can resolve these issues.

Final Thoughts

When a compressor is shutting itself down again and again, it’s not doing it at random. 

Track the issue back to the source, a blocked cooler, an unstable supply, a sensor that’s no longer reading correctly, and the machine can run as it should. 

Performance improves, reliability follows, and those repeated shutdowns stop becoming part of the day.

Stop shutdowns before they happen. Our Guardian Scheduled Maintenance Plans are made to stop these common types of failure, so your system stays compliant and reliable.

Is your production being hurt by air compressor downtime?

Control Gear provides expert support and diagnostics across South Wales and the West. 

Speak to our technical team to talk through what’s happening on your system, and what we can do to keep it running reliably.