If an air compressor won’t start, it points to a problem within its control or mechanical systems. Modern systems are designed to stop the startup process if safety limits are exceeded, preventing the unit from running unsafely. To find the root cause, you need to check the electrical power supply, the control circuit components, and the mechanical load.
Safety & Compliance
Contemporary air compression systems, such as Atlas Copco machines, are equipped with Elektronikon controllers which employ “Start Inhibits” to stop your equipment from functioning beyond safe boundaries. This function complies with the Pressure Systems Safety Regulations 2000 (PSSR).
These regulations mandate a Written Scheme of Examination to outline operational boundaries. If a safety valve activates because of overpressure, the equipment must not be restarted until a qualified individual examines the vessel.
Disregarding these lockout breaches PUWER (Provision and Use of Work Equipment Regulations 1998). PUWER requires that equipment is kept in functioning condition. Overriding safety mechanisms to initiate operation is dangerous. Always follow Lockout/Tagout (LOTO) protocols prior to examining parts.
Could the Problem Be Due to the Electrical Supply?
The most frequent cause of a non-starting compressor lies in the 415V three-phase supply.
What is Single Phasing?
Single phasing occurs when one of the three supply lines disconnects, which is often due to a blown fuse on the distribution board. The electric motor in your unit may emit a humming noise but will not turn on, because doing so would cause a high current draw and trigger overload protection.
Does Voltage Imbalance Affect Startup?
A voltage imbalance of just 2% between phases causes a higher current imbalance which overheats windings. Controllers will detect this imbalance and inhibit starting to protect the motor. Power fluctuations from other heavy plant machinery can also trigger under-voltage lockouts, and a faulty pressure switch will also interrupt the start signal, especially on older compressor assemblies.
What Is a Phase Sequence Error?
Rotary screw compressors must rotate in one specific direction, and if maintenance work on the distribution board swaps two phases, the Phase Sequence relay will detect the error. It will then open the control circuit to prevent the air end from running in reverse and the display will typically show a “Phase Sequence” error.
How Do Control Panel Faults Block Operation?
The Elektronikon controller manages the compressor’s logic by distinguishing between “Warnings” and “Shutdowns”; warnings allow operation, but shutdowns prevent the motor from starting.
Common Fault Codes
- F21 Motor Overload: Indicates the thermal overload relay has tripped due to high current.
- F15 Fan Overload: The cooling fan is blocked or seized, preventing the main motor from starting.
- Sensor Failure: A broken wire to a pressure or temperature sensor triggers a safety shutdown.
What is Thermal Lockout?
A thermal protection module monitors motor winding temperature so that when the motor overheats, it can prevent a restart until the windings cool down. Cooling can take up to 30 minutes.
Why Won’t the Start Button Work?
If the compressor is integrated into a factory network (LAN), the local start button is often disabled, and the controller will wait for a signal from a master sequencer. Additionally, Service Interval Lockout prevents startup on newer Atlas Copco controllers when maintenance is overdue.
Can Mechanical Resistance Prevent Startup?
Mechanical issues can physically stop the compressor motor from turning or cause overload trips.
How Does the Unloader Valve Affect Startup?
The unloader valve controls air intake and must be closed during startup to allow the motor to reach speed without load. If the unloader valve gets stuck open, the compressor will attempt to start against load, but as the motor cannot overcome this resistance, it will cause an overload trip.
What Causes Back Pressure?
The Minimum Pressure Valve (MPV), or tank check valve, prevents system air from flowing back into the compressor. A malfunction in the check valve can cause the compressor to retain pressure, leading to the compressor refusing to start. If this valve fails, the separator tank will remain pressurised, and the motor will stall against the load.
Is the Air End Seized?
A seized air end or motor bearing will prevent the motor from turning and it may hum briefly before the breaker trips. This will require major repairs or an air end swap.
How Do Environmental Conditions Affect Startup?
The UK climate presents specific challenges for air compressors.
What is Cold Start Syndrome?
The reduced ambient temperatures during a UK winter increase oil viscosity, and in an unheated plant room the thickened oil causes resistance on the rotors. The motor will consume extra current to rotate the element and will frequently trigger the overload relay. Selecting the best compressor oil for your surroundings is essential to avoiding this resistance.
Can Moisture Lead to Failures?
Condensation forms on Printed Circuit Boards (PCBs) and contactors in damp environments, which causes short circuits and blown control fuses. Moisture in control lines can freeze and stop the unloader from operating, and a faulty pressure release valve can trap residual pressure in the separator tank, increasing the starting torque.
How Do VSD Faults Stop Compressors?
Variable Speed Drive (VSD) compressors use complex power electronics.
What are DC Bus Faults?
The VSD converts AC power to DC. If the incoming power supply is unstable, the DC bus voltage will be incorrect and the drive will inhibit the output to protect itself.
Why Does Converter Overtemperature Occur?
Blocked cabinet filters reduce airflow and will cause the drive to overheat, so the VSD module triggers a “Converter Overtemperature” alarm, which prevents the unit from turning on. These VSD-related faults represent common air compressor issues on modern industrial systems.
How Can I Troubleshoot and Prevent These Issues?
Follow a logical diagnostic process.
- Check Safety: Ensure E-Stops are released and the display is active.
- Verify Power: Check for 415V across all three phases.
- Inspect Display: Look for specific codes like F21 or “Phase Sequence”.
- Check Oil Level: Low oil levels trigger safety cut-outs.
- Listen: A humming sound indicates a seized motor or single phasing.
- Reset: Attempt a manual reset of the overload relay if safe.
Preventative Maintenance Schedule
The British Compressed Air Society (BCAS) recommends specific checks to prevent startup failures.
- Daily: Drain condensate to prevent hydraulic lock and check oil levels.
- Weekly: Inspect the air intake filter because a dirty air filter will increase startup strain.
- Monthly: Check electrical connections for tightness to prevent arcing.
- Yearly: Replace the Air Compressor Pressure Switch or sensors if they show drift.
On piston compressors, a failed start capacitor will stop the motor from reaching operating speed.
How Can J Ll Leach Help?
Resolving a non-starting compressor often requires specialist intervention. At J Ll Leach, we offer comprehensive support across Stoke-on-Trent, Birmingham, and Shrewsbury.
Emergency Repair and Hire
J Ll Leach provides 24/7 emergency breakdown support across the Midlands, and if a repair requires workshop time, we offer hire compressors to maintain your air supply during our repairs.
Atlas Copco Expertise
As a Premier Distributor for Atlas Copco, we supply genuine OEM parts for GA, G, and ZR/ZT series machines. Our engineers are also trained to diagnose Elektronikon faults and VSD issues accurately.
SMARTLINK Monitoring
We install SMARTLINK technology to provide remote health monitoring. SMARTLINK flags abnormal temperatures, currents, and pressure trends before they cause a shutdown, allowing for proactive intervention.
Conclusion
A compressor that won’t turn on is an operational issue that demands a methodical approach. From checking a blown fuse to diagnosing a seized air end, understanding the root cause is essential. Regular maintenance and compliance with Daily Operation Compressor Safety Checklist procedures reduces the risk of unexpected downtime. For immediate assistance, or to discuss Ignoring Air Compressor Maintenance risks, contact the J Ll Leach team today.
Get Your Compressor Running
- Contact us for 24/7 emergency repair in the Midlands.
- Book an air audit to identify system weaknesses.
- Browse genuine parts to maintain your equipment warranty.