Fault Finding on Your Piston Compressor

If your piston compressor is not working properly or your ABAC machine is faulty, this air compressor troubleshooting guide is for you.
Piston compressors are fairly simple in the way they work but like anything electrical or mechanical things sometimes go wrong. Unfortunately it’s usually at an important time when you most need it.

A lot of faults with piston compressors can be traced back to the way it was installed so it’s worthwhile checking our installation guide.  If your equipment was not properly installed you might be able to set it up again and troubleshoot the problem.

You will find information about common faults and some checks you can carry out yourself in the list below. If you have an electrical fault with your air compressor you will need someone qualified to fix it. You can either call a qualified electrician or contact your nearest ABAC approved distributor.

Reduction in output, machine running all the time, performance has deteriorated over time

  • Air filter blocked – if the machine can’t breathe it can’t compress and deliver air. Start with a quick check to see if it is blocked and a clean may help.
  • Drive belt(s) slipping – does the machine sound normal? If your drive belt is slipping, you will probably hear a squealing noise and the reduced speed on the pump unit reduces the usual noise level. Stop the unit and make sure it is isolated from the mains power supply. You might find that you can solve the problem by adjusting the belt tension. It is a good idea to check the belt tension on a regular monthly basis. If you let the belt run slack over a long period of time, you might damage the belt and pulley.
  • Air leaks on pipework / hoses. Close the outlet valve on the compressor and see if it now builds up to pressure and stops. If this does happen, there is a good chance you have air leaks downstream of the outlet valve. Because you can’t see air leaks, people often ignore them and forget that they cost you money. It takes electricity or fuel to generate compressed air so don’t waste it! You can order new pipes and hoses from ABAC. Just ask our LiveChat team for help.
  • Has your air demand increased over time? If you have added extra air tools or larger air tools, your current machine might be struggling to keep up. If your business has grown since you installed your air compressor, you might need to upgrade. You can look at our handy guide to upgrading your air compressor or go straight to our online air compressor shop. As always, the LiveChat team is here to help.
  • Head gasket blown or broken valve plate. The gasket or valve plate on your air compressor works very hard. It opens and closes countless times and it experiences endless temperature changes. It’s not surprising that these parts sometimes fail. You will notice that the unit is down on flow output along with an increase in operating temperatures. On a two stage compressor the intercooler pressure relief valve will possibly blow off. This indicates overpressure as a result of a failed valve within the cylinder head. Ask our LiveChat team about buying service kits and performance kits or contact your nearest ABAC approved distributor. You can get all the necessary parts to bring your air compressor back to peak performance. We recommend a yearly service on a machine that is in regular daily usage. This also reduces the risk of breakdown. All of our distributors can put together service plans to give you peace of mind and reliability.

Air leaking from around the base of the pressure switch.

  • Air leakage on initial start-up, empty air receiver. The valve acts as a delay valve to allow the machine to start. Once it reaches 10-15 psi within the air receiver it automatically closes. This is normal and a design feature of the piston compressor.
  • Air leakage whilst running after the initial start period. If the air continues to leak after the compressor has started, you know you have a faulty valve. You will need a new pressure switch as the valve is an integral part of the switch.
  • Air leakage when the machine has stopped. When your compressor stops, it will release some air. This is normal. The compressor needs to release the air so it is ready to restart again. (This is similar to when you put a car into neutral so you can start the engine without any load on it). You shouldn’t hear any more air leaking from the system after this. If there is still air leaking from the pressure switch it means the non-return valve has failed. You will need to buy a new pastel fitting. Either ask our LiveChat team for help or contact your nearest ABAC approved distributor


  • Does your machine have enough clearance around it? You need enough space for air to flow over the compressor and cool it down. You need a space of 300-400 mm clearance between the wall and the compressor to ensure there is enough airflow.
  • Our patented belt guard design ensures ABAC air compressors cool correctly and allows the machine to operate at lower temperatures. You need to examine the apertures of your system to see if they are blocked.
  • If you install a machine in a cupboard to reduce the noise level you are more likely to have problems with overheating. We have an excellent range of low noise silenced units which are a much better solution. We design quiet air compressors to run in an enclosed metal cabinet with additional cooling fans and dedicated air channels to keep them cool.
  • On three phase 415 volt supplies incorrect phase rotation can cause the machine to run the wrong way reducing the cooling effect by 30-40%. Check the rotation at the commissioning stage and if it is incorrect ask your electrician to change the phase rotation. This will ensure optimum cooling and longer life. If your unit is running the wrong way, you can often see an oil mist around the filler plug / breather on the front of the pump unit.

Motor tripping on thermal overload or blowing fuses

  • Machine trying to start against pressure. If your compressor tries to start against pressure, you probably have a faulty non-return valve leaking back or faulty pressure switch. Read the section on air leakage from pressure switch (above). This describes how the pressure switch and non-return valve should work together. If the air fails to unload or blow down when stopped it is similar to attempting to start your car in gear.
  • Do not operate piston compressors off extension leads. You should not run your compressor on an extension lead as they use too much current. If you exceed the thermal cut out set value or the fuse rating then it will activate or blow. This fuse is designed to protect your compressor and indicates that something isn’t right. You must remove the extension lead and put the compressor close to the electrical supply. You can get compressed air where you need it if you extend the airline. Ask our LiveChat team or contact your nearest ABAC approved distributorfor help.
  • As a rule, any of our piston compressors supplied with a fitted 13amp plug are designed to operate off a 13amp socket. If you buy an air compressor with a cable which requires wiring to a plug, you need a 16amp or 32amp supply. You will need a qualified electrician to connect your compressor to the appropriate electrical supply.
  • Fuses or circuit breakers should be either HRC or Type D designed for motor starting – Type B are used on lighting circuits and Type C on general protection. It is surprising that we still find electrical contractors adamant that a Type C breaker is right for the application so you need to make sure the correct one is installed.

Water in airlines

All compressors will generate water as a result of the compression process. Ambient air is relatively humid when it enters the compressor. The air cools within the air receiver and the water condenses out of it. You must drain the air receiver every day and fit a water separator to reduce the level of water in the airlines. If you need to fully remove bulk water and water vapour which could condense within the airlines you will need a dedicated dryer. These are either the refrigerant type for general use or the desiccant type for critical applications which require a negative pressure dewpoint (Dental compressors and compressors used on food or pharmaceutical applications typically).

We hope this general air compressor troubleshooting guide will help you to keep your ABAC air compressor running smoothly. Please remember that we can only provide general checks on electrical faults for you to carry out. If these don’t help, it is time to call in a qualified electrician or contact your nearest ABAC approved distributor.

The best way to avoid faults is to install your air compressor system properly. Install your compressor correctly on day one to keep your new ABAC piston compressor reliable. Follow our service schedule and carry out the regular checks we recommend and you will have trouble free operation for many years.