When air compressors suddenly stop functioning, it can be very frustrating. They ultimately cost money, halt production lines, and lengthen order processing times. But most of the time, the machine is trying to say something.
The Atlas Copco GA series and other newer compressors have safety systems built in. A compressor will typically shut down unexpectedly to protect itself from a major issue, such as an electrical fire or a blocked airend.
To get back online, you must understand why this is occurring. A professional engineer may be required to address certain issues, but being aware of the symptoms can help you identify the issue more quickly.
Trip vs. Shutdown: What Is the Difference?
When you look at the controller display, the specific wording matters. Technicians distinguish between a “trip” and a “shutdown,” and knowing the difference helps pinpoint where to look.
A trip is usually an immediate, hard stop. This happens when a safety device, like a motor overload relay or circuit breaker, activates instantly to cut the power. It suggests a significant electrical surge or a mechanical blockage that poses an immediate danger.
A shutdown is a more controlled sequence. This happens when the compressor’s central controller (PLC) sees that a sensor reading, like temperature or pressure, has gone above a safe level. The machine will stop to avoid damage, but it usually keeps the exact data point that caused the problem, which makes it easier to fix.
Common Fault Areas That Cause Shutdowns
There are a number of common reasons why a compressor might stop working, from simple problems with the environment to more complicated problems inside the machine.
1. Overheating and Thermal Issues
Overheating is easily the most common reason we see for unexpected shutdowns. When you compress air, it makes a lot of heat. If the oil system can’t get rid of it quickly, the temperature goes up quickly.
Most Atlas Copco units will warn you when the temperature reaches about 110°C and shut down completely at 120°C to keep the parts inside safe.
- High Room Temperature: The compressor recycles its own hot exhaust air if the plant room is too hot or doesn’t have enough air flow.
- Clogged Coolers: In dusty environments, the cooler matrix can become blocked. This creates a “wool blanket” effect where airflow cannot pass through the fins to cool the oil.
- Thermal Valve Failure: The oil circuit has a thermal valve that controls the temperature. If the wax element inside breaks, the cooler might not open, which means that hot oil will go around it completely.
- Low Oil Level: Oil acts as a coolant. If the level is low, there isn’t enough fluid to absorb the heat.
- Minimum Pressure Valve (MPV) Fault: If this valve gets stuck, the system might not be able to build up enough internal pressure to move the oil around, which could cause the temperature to rise quickly.
2. Electrical Faults and Power Supply
Industrial compressors in the UK generally operate on a 400V three-phase supply. They are sensitive to the quality of that incoming power.
- Phase Imbalance: If the voltage between the three phases is off by even 2%, the motor can overheat and shut down.
- Loose Connections: Over time, vibrations can make electrical terminals come loose. This makes things harder to move and makes heat, which can trip thermal relays.
- Star-Delta Timing: Big motors start in a “Star” shape to lower the current, and then they switch to “Delta” to run. If the timer breaks during this switch, the machine will stop.
3. VSD Specific Faults
Variable Speed Drive (VSD) compressors are excellent for energy efficiency, but they add a layer of complexity. The drive itself is essentially a computer with its own needs.
- Internal Fan Failure: The VSD inverter generates heat and has its own small cooling fans. If these fail, the drive will trip on “Drive Over-temperature,” even if the main motor is cool.
- DC Bus Overvoltage: This is an electrical fault often caused by spikes in the mains supply or rapid deceleration of the motor.
4. Pressure and Mechanical Control Failures
The compressor must be able to smoothly “load” (pump air) and “unload” (idle). Safety mechanisms take over if the control loop fails.
- Pressure Switch Malfunction: If a mechanical switch breaks, it might not tell the compressor to stop when the tank is full. The safety valve will eventually rise up to let the extra pressure out.
- Inlet Valve Sticking: The unloader valve controls air intake. If it gets stuck open, the compressor keeps pumping indefinitely until it trips on high pressure.
- Belt Tension: A loose belt can slip on belt-driven units like the GX series. This slows down the element, which confuses the controller and causes a problem.
5. Filtration and Blockages
If the air or oil cannot flow freely, the motor has to work much harder to push it through.
- Separator Blockages: The oil separator element removes oil from the air. If it gets clogged, it creates a high differential pressure ΔP. This acts like a brake on the system, causing the motor to draw high amps and trip.
- Scavenge Line Issues: If the line that recovers oil from the separator is blocked, oil carries over into your pipes. This drops the sump level and leads to overheating.
Atlas Copco Model Specifics
If you are operating Atlas Copco equipment, the diagnostic process is often easier thanks to the smart controllers.
GA and GA+ Series (Rotary Screw)
These machines use the Elektronikon controller. It acts like a black box recorder. You can check the “Saved Data” to see exactly what the motor current and element outlet temperature were at the moment of the shutdown.
VSD+ Series
These are distinct because of their upright, compact design. The motor is a permanent magnet type, and the drive is integrated into the housing. Faults here often relate to the “Converter Outlet Temperature,” so it is vital to keep the electrical cabinet filters clean.
SMARTLINK™ Integration
Many modern units are connected to Remote Monitoring (SMARTLINK™). This is a huge advantage because it tracks trends. SMARTLINK can let you know that your discharge temperature has been slowly rising over the past week, so you can fix it before the machine stops instead of it stopping all of a sudden.
Troubleshooting Workflow
If your compressor isn’t working, follow these steps to safely figure out what’s wrong. Please remember that the Electricity at Work Regulations say that only a qualified person should do live electrical tests.
- Check the Display: Before you press reset, look at the controller. Navigate to the history log to find the specific error code (like E16 or F21).
- Check the Oil: Look at the sight glass. Is the level correct? Does the oil look milky (water contamination) or dark and thick (varnish)?
- Inspect the Room: Is the plant room significantly hotter than usual? Are the intake louvres on the compressor free of dust?
- Listen at Start-Up: If it is safe to do so, start the machine. Listen for the “clunk” of the contactors switching over. It should sound smooth.
- Watch the Pressure: Ensure the compressor stops pumping (unloads) when it hits the target pressure.
- Verify the Sensors: Sometimes sensors fail. If the screen says 120°C but the pipe feels cool to the touch (be careful!), you might just have a faulty sensor.
You can read our guide on Common Air Compressor Problems and How to Fix Them to get a more in-depth look at how to fix these problems.
UK Compliance & Safety Warning
It can be tempting to “tweak” the settings when you are under pressure to start production. You must be aware of UK safety regulations, though.
Under the Pressure Systems Safety Regulations (PSSR 2000), your system has a Safe Operating Limit. You must never adjust pressure switches or safety valves to bypass a tripping issue. Doing so is dangerous and invalidates your Written Scheme of Examination. If you are unsure about your compliance obligations, our team can help with PSSR Consultation.
Similarly, under the Electricity at Work Regulations 1989, opening 400V panels for diagnostics carries risks. If you aren’t trained, it is safer to call a professional.
When Specialist Intervention Is Required
While checking filters and ventilation is good practice, some faults require a qualified engineer. You should call for support if:
- The compressor trips the moment you press the start button.
- The controller displays a specific VSD or Inverter fault.
- You suspect the airend has physically seized (locked rotor).
- The safety valve keeps lifting despite your adjustments.
At Design Air (Scotland) Ltd, we are based in Airdrie and support businesses across the Central Belt and Scotland. We provide a 24/7 Compressor Repair Service because we know that when air stops, production stops. Our engineers carry the diagnostic tools for Atlas Copco, HPC, and CompAir units, along with the common parts needed to fix thermal and electrical faults on the first visit.
If a repair is going to take longer, we also have a Hire Equipment fleet to fill the gap and keep you operational.
To avoid these breakdown headaches entirely, many of our clients choose a proactive Air Compressor Service Plan. Regular maintenance finds worn parts, like the wax element in the thermal valve, before they cause a shutdown.
Frequently Asked Questions
Why does my compressor keep tripping the breaker?
This usually points to a high current draw. A “locked rotor” (mechanical seizure), a short circuit in the motor windings, or a big imbalance in your power supply could be the cause.
Why does my compressor shut off after a few minutes?
The classic indication of a thermal shutdown is this. The machine functions properly up until the oil becomes hot, at which point the cooling system is unable to quickly dissipate the heat. The issue is frequently a blocked cooler or a broken thermal valve.
What is the normal operating temperature for a screw compressor?
Most units work best when the temperature is between 75°C and 90°C. When it reaches 110°C, you will usually see a warning on the screen.
Can I bypass the pressure switch to keep running?
No. This removes your primary safety control. It is illegal, dangerous, and can lead to a catastrophic failure of the pressure vessel.
Is your compressor switching off unexpectedly? Contact Design Air (Scotland) Ltd today for rapid diagnosis and repair across Scotland.
