Air Compressor Trouble Shooting Guide- What’s Wrong with my Compressor?

It’s late at night or a weekend and you’re knee deep in a project ready to call in some pneumatic power to help you speed up your progress and the air compressor starts acting up! What can you do?! You can either give up and call in a professional; or maybe diagnosis and fix the issue yourself like a true Eastwood Guy or Gal! We decided to put together a simple trouble shooting guide for common reciprocating air compressors to help you get to the bottom of your problems.


Compressor Won’t Start

If you’re compressor is dead in the water and won’t show any signs of life (clicking, humming, sparks, fire, etc.) you may have a switching or electrical issue. Generally speaking, when a compressor pump or electrical motor goes bad it will give you some warning before it totally dies. It will make odd sounds or you will see a big drop in performance, etc.

Start at the furthest point from the compressor and work your way through the compressor. Check the fuse box that feeds the compressor and make sure there are no breakers partially flipped or completely switched to off. Try switching the breaker back and forth and test the compressor. This is the easiest, quickest solution. Keep in mind that a flipped breaker usually means there may be another problem that may arise in the future. If the breaker continuously flips discontinue use of the compressor until you can locate the problem. If the breaker on the wall looks ok, make sure your compressor itself doesn’t have a breaker mounted on it or near it on the wall. Follow the same procedure here as above.

Next let’s check the pressure switch on the compressor itself. The pressure switch senses the tank pressure and shuts the motor off to avoid over-pressurizing the tank. Check the pressure gauge on your tank and make sure it is below the switch setting. If the pressure switch is set to 125psi it should allow the compressor to turn back on at anything below that pressure. Most pressure switches can be tested manually by removing the cover and activating the pressure switch lever with your finger. This will override the switch and turn the compressor on. If you’re able to manually activate the switch and make the compressor run you now know that your switch is out of adjustment or needs to be replaced.

If the switch isn’t working manually you must next check the wiring and make sure that there is power going to the switch. Check the wiring diagram for your switch and make sure all wiring is getting power and isn’t broken from the switch to the motor. Replace or repair as necessary.

Finally Check that your compressor will turn over by hand. Most reciprocating compressors have pulleys that can be turned by hand. You may need to remove a cover/guard to get to them. Unplug your compressor at the wall outlet and try and to turn the larger pulley by hand. It should turn both the compressor pump pulley and electric motor pulley at the same time. If you aren’t able to turn both pulleys by hand you may have a seized electric motor or pump. Check them separately to find the issue. Running a compressor out of oil can seize the engine (much like your car) or a bad bearing in an electric motor can seize it and cause a no-start issue.


Loud NOISES!! 

Much like any reciprocating engine there will be noise. But you shouldn’t hear loud noises from your compressor. If you hear it, you need to check on it before it gets worse. If your compressor is in a hidden area (outside, separate room, etc) it’s good to go check on it from time to time to make sure that no odd sounds are coming from it.

Check all of the parts related to the external moving parts of your compressor. First thing is the guards over the pulleys and belt. Is it rattling or loose? You’d be surprised how loud a loose belt guard can be when combined with the sound of your compressor! Also check the belt and pulleys on your compressor. The belt should be moderately tight with little slack. Pulleys on the compressor pump and the electric motor are normally keyed so they shouldn’t come loose, but occasionally we’ve seen the end lock bolt on the pulleys come loose and cause a loose pulley that will make a racket when spinning. This is a good example of checking loud noises immediately when you hear them; a loose pulley can wobble and damage the pulley bore, key way, or shaft if left loose too long.

Next check how the compressor tank, pump, and electric motor are sitting. Has anything shifted so that it is resting against the compressor? Are the rubber dampeners or rubber feet on the compressor pump, motor, etc broken, cracked, loose? A loose or damaged rubber dampener will cause vibration and excessive noise if left alone too long.

If those simple things aren’t the issue listen to the compressor as it fills from empty; does it change as it builds pressure or gets hot? A bad valve could cause excessive noise only above a certain pressure or temp. Bearing, piston ring, or some other internal issue may also worsen as the pump warms up. Be sure you check your oil levels. Running a compressor low or out of oil can cause catastrophic damage and could mean a pump replacement if left too long. You can also drain the oil and check it for any signs of metal to give you an idea if something major has happened. A piston ring issue will cause excessive oil consumption and a rod or main bearing issue in the pump will generally cause a knock or RPM-based sound. Most compressor pumps can be rebuilt if the issue is caught early enough. Check with your compressor manufacturer for those parts.

Loud hissing or excessive air leakage sounds mean that you have a leak somewhere at a fitting or an unloader valve is damaged and is allowing air to go where it shouldn’t. Check to make sure that your pressure switch is shutting the compressor off at the appropriate PSI and isn’t over pressurizing the tank causing the unloader valve to be tripped.

Compressor Tries and Tries (and Fails)

Can you hear the compressor attempting to turn, but it can’t get started? Does it trip the breaker after trying? This could be caused by a number of issues. As mentioned in earlier steps, test to make sure that you can turn the compressor pulleys over by hand. A seized pump or motor can cause this issue. If your check valve at the tank goes bad it will allow the pressure in the tank to work back into the compressor pump head and will become too much pressure for the electric motor to overcome and spin the pump. This is easy to diagnosis as the compressor will often run fine through it’s first cycle (or part of it) and then it will stall or fail to start and trip the breaker due to the force to start up. The majority of the draw of an electric motor/reciprocating engine is when it first starts and if there is additional force on it from pressure in the compressor pump it will trip the breaker. Check valves are normally threaded into the top of the air tank or somewhere between the tank and the compressor pump outlet. Replacement is cheap and simple and can be done quickly with normal hand tools.

Check your oil level. Low oil can cause the compressor to seize and fail to start when you try to turn it on. Most compressors have a sight glass to check oil levels quickly. If the compressor has been run very low or completely out of oil it could seize the pump and require a rebuild or replacement.

Air Compressor won’t build Pressure 

If your compressor suddenly won’t build pressure or hasn’t been maintaining the pressure it used to there are a couple things you can check. First make sure that your pressure switch is cutting out at the correct PSI. A faulty switch could start shutting the compressor off at a lower pressure than you want and will cause a “no-pressure” issue. If you’re compressor just seems to run and run and never build enough pressure it could have a large leak that it is causing the air to leak out as quick as it is entering the tank. Check and repair anywhere you hear a leak coming from. It also could have a bad inlet/outlet valve or reed valve that isn’t allowing the pump to build pressure. This may require disassembly of the pump head to check. Finally check your inlet filter(s) as over time they can get clogged from breathing shop dust and dirt and can get clogged so much that the inlet air is restricted choking the compressor down. Replacing your intake filter(s) every year or two is good insurance if your compressor lives in your work space.

Water In the Air Lines

A natural by-product of compressed air is moisture or water. The amount is dependent on the heat of the air coming out of the compressor and the climate you’re in. Remember to drain the water from your air tank regularly. There is a drain on the bottom of your tank that can be loosened and drained periodically. We also suggest installing an air dryer or air filter system that will reduce the moisture in the air lines at your outlet or tool. Keep in mind that early symptoms of a failing compressor could be a sudden influx of water into your air lines because the compressor is working harder or longer and heating up the air more than usual.

Excessive Oil in Air Lines

Just through the process of compressing air your pump may put a small amount of oil in the air. This is normal and an air filter system can help separate the oil in the lines. If you begin to see oil seeping out of air lines or at the outlet of your air hose your compressor pump may be experiencing blow-by and may need a rebuild due to failed piston rings. We’d suggest an air filter system first, but if that can’t keep up you may have a larger issue you need to look into.


We hope that these tips will help you diagnosis an issue with your air compressor and help you save money by repairing them yourself. Reciprocating air compressors are fairly simple machines and most home DIY’ers can handle the diagnosis and repairs. You can view our entire line of air compressors and accessories here: 

Leave a Reply

Back to top button