Through this website I have helped hundreds of people from all over the world with their compressor repair and troubleshooting questions.

Here are some of the most frequently asked questions and the most common reciprocating compressor problems.

You are now on the reciprocating / piston compressor troubleshooting page, but there's also the rotary screw compressor page and the portable (diesel) compressor page.

Common Reciprocating Piston compressor problems

Common reciprocating piston air compressor problems

Compressor is dead - nothing happens

If really nothing happens (no sounds, no click), it is most probably an electrical problem. Check the following:

Power supply - check if there is power and all fuses are ok.
Pressure switch - check the setting on the pressure switch and the actual pressure in the tank. Check the electrical connections on the pressure switch. Most pressure switches can be operated (tested) by pushing on the lever. Does the compressor start?
Low oil level or high temperature safety switch - Bigger compressors have safety switches for low oil level and/or high (overload) temperature. They will prevent the compressor from starting. Sometimes they have a reset button.

Compressor is making noise

Check where the noise is coming from. Check if everything is fixed tight. Look for loose belts, loose bolts, loose pulleys. Are the rubber damping feet still ok? If the sound comes from the compressor itself, check the oil level first. If the sounds appears or disappears at a certain level, check the inlet/outlet valves, piston rings. If it is a knocking type sounds, you may have a problem with your main bearings or connecting rod bearings.

High oil consumption / low oil level

The oil must go somewhere. Check where the oil is going to.

Oil leak
High oil carry over = oil in compressed air (see next point)

Look for the leak. Common points are the drain valve/plug and the shaft seal.

Oil in compressed air

This can have a lot of causes.

Too high oil level. When the oil level drops to normal levels, oil carry-over will stop
Wrong oil. Oil with a too low viscosity, or not suitable for reciprocating piston compressors (no, you can't put 15W40 motor oil in your air compressor!)
Too high running temperature. A higher temperature will lower the oil viscosity (it becomes thinner), which results in more oil carry-over
Worn piston rings or wrongly installed
Worn cylinder surface

Compressor not building pressure and air blowing out of the inlet filter

The inlet check valves / plates are broken, worn or dirty. At the up-stroke, air is pushed back through the inlet filter, instead of to the next stage / air receiver Pressure builts up very slowly (low capacity) Either the compressor is not pumping at full capacity, or you have a big leak somewhere. First, check for air leaks. If nothing found:

Check inlet/outlet valves (inside compressor head)
Check head gasket
Check inlet air filter

Compressor can not start (but tries hard).

If you're compressor is unable to start up, but it isn't able to, you most probably have a problem with your unloader valve. When the compressor stops, the unloader valve blows down the pressure in the exhaust pipe of the air compressor. This is to make sure that the compressor is able to start up again.

If the pressure remains in the exhaust pipe, the air pushes down on the compressor piston and the motor is unable to get it moving.

When compressor is stopped, air is leaking out of the unloader valve/pressure switch

There is nothing wrong with your unloader valve or pressure switch. The problem is with the check-valve on the air receiver. The unloader valve blows-off the exhaust pipe of the air compressor. The check valves makes sure that the air in the air receiver stays in the air receiver.

High cylinder temperature.

Can be any of the following:

High ambient temperature
Broken cylinder head gasket
Leaking/broken/dirty intake/exhaust valves

Water in compressed air

Water is a normal by-product of air compression. Your air receiver should have a drain valve. Drain the drain valve until all the water is out. If you have an automatic drain valve, check if it is working correctly. Thermal relay / overload relay trips Could be either an electrical problem or a mechanical problem. Check with a current clamp meter how much amps the motor draws. Compare to nameplate data.

Check by hand if you can turn the compressor (switch compressor completely off). Check the voltage. If the voltage is too low, it can result in overload/overheating. Also check the voltage when the compressor is running. If the voltage drops significantly, you used a too long extension cord, or to thin electrical wiring.

'Screaming' sound, especially when compressor starts up.

Belt is too loose. Tighten belt or replace with new one.