Fault Finding on Your Piston Compressor

If your piston compressor is not working properly or your ABAC machine is faulty, this fault-finding 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 fix the problem.

Some of the most common faults are described below and where possible we have provided some checks for things you can do yourself. However when it comes to electrical faults you will need to call in a qualified electrician or a qualified compressor service engineer.

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. A quick check to see if it is blocked and a clean may help.
  • Drive belt(s) slipping – does the machine sound normal, slipping dive belts are usually accompanied by a squealing noise and the reduced speed on the pump unit will reduce the usual noise level. Stop the unit and ensure it is isolated from the mains power supply – a quick check of the belt tension and adjustment may solve the problem. It is worthwhile checking belt tension on a regular monthly basis – longer term damage to the belt and pulley can occur if left to run with a slack belt over a long period.
  • Air leaks on pipework / hoses – close the outlet valve on the compressor and see if it now builds up to pressure and stops. If it does then there is a good chance you have air leaks downstream of the outlet valve. Air leaks can’t be seen only heard – on a machine delivering 10cfm what you might think are negligible leaks when added together can become quite significant. It’s also costing you money to generate this compressed air in terms of electrical power. The chances are if it was a water or hydraulic oil leak it would be noticed and fixed!
  • Has the air demand increased over time? – adding extra air tools or larger air tools can result in the machine struggling to keep up with the increased demand. If the machine has been installed for a number of years and your business has increased in time with more users then it could be a case you have outgrown the compressor. In this case, it’s time to upgrade.
  • Head gasket blown or broken valve plate – over a period of time and countless opening and closing of valves alongside temperature changes it’s not surprising that a gasket or valve plate will 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. You can buy service kits and performance kits for all our machines with all the necessary parts to bring your machine back to peak performance. We recommend a yearly service on a machine that is in regular daily usage. If you fit the service kit at the recommended interval you will avoid that breakdown situation. 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 – this valve acts as a delay valve to allow the machine to start, once it reaches 10-15 psi within the air receiver it will automatically close. This is normal and a design feature of the piston compressor.
  • Air leakage whilst running after the initial start period – if the air leakage is continuous it indicates the valve is faulty. You require a new pressure switch as the valve is an integral part.
  • Air leakage when the machine has stopped – when it first stops the machine will exhaust some air. This is normal and it allows the air to be removed from the compressor so it is ready to restart again (it’s similar to putting the car into neutral to allow the engine to start without any load on it). Once stopped and the initial unload has taken place no leakage should be coming from the pressure switch – if it is the non-return valve has failed and requires a new pastel fitting.


  • Ensure your machine is installed with enough clearance around it to allow correct cooling airflow over the compressor. 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. Examine your system and make sure the apertures aren’t blocked, the unit isn’t too close to the wall and there is an adequate air supply?  Installing a machine within a cupboard to reduce noise levels is a common cause of overheating problems. The correct solution is one of our low noise silenced units which have been designed to run within an enclosed metal cabinet with additional cooling fans and dedicated air channels for optimum cooling.
  • 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. An indication that the unit is running the wrong way can be seen by 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 – this is usually caused by 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.
  • Piston compressors aren’t designed to operate off extension leads – operating on an extension lead will result in an increase in the current drawn and if it exceeds the thermal cut out set value or the fuse rating then this will activate or blow. This fuse is designed to protect the compressor and indicates that something isn’t right. Remove the extension lead and move the compressor close to the electrical supply and extend the airline and you will fix the problem.
  • As a rule, any of our piston compressors supplied with a fitted 13amp plug are designed to operate off a 13amp socket. Any machines supplied with a cable which requires wiring to a plug are for a 16amp or 32amp supply. These should be connected to the appropriate electrical supply by a qualified electrician.
  • 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. The ambient air is relatively humid when it is drawn into the compressor. When the air is cooled within the air receiver, water will condense out of it. Drain the air receiver on a daily basis and fit a water separator to reduce the level of water seen within 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 guide will help you to keep your ABAC air compressor running smoothly. It is designed to help you within general boundaries of day-to-day operation. Please remember that we can only provide general checks on electrical faults for you to carry out, once these are exhausted then it is time to call in a qualified electrician or compressor service engineer.

As we stated at the beginning of this general fault finding guide, the majority of faults we come across tend to be related to the quality of the installation. Get your compressor correctly installed on day one and you will ensure reliable operation of your new ABAC piston compressor. If you also follow our service schedule and recommended regular checks you will ensure trouble free operation for many years.