Air Compressor Not Turning On?

So your air compressor is not turning on? Well, the most common errors that lead to an air compressor not working include bad electrical connections, bad circuit boards, and faulty parts (fans, filters, bearings). The easiest way to figure out how to troubleshoot a problem with your air compressor is to break down the process step by step, so our guide below will walk through the steps to diagnose your issue. This will help you identify what part of the machine is malfunctioning.

So, is the compressor switch on?

I know it sounds stupid, but this is by far the most logical place to start! If your air compressor has an ON/OFF switch, either separate or part of the pressure switch, just make sure you it is actually switched on!

It is likely that the power switch will be on if you have been using the compressor and it will not start. Nevertheless, you should check it anyway.

For air compressors, power requirements will vary considerably from one model to another. Basically, there are those that run off electricity and others that run off fuel in order to secure power. In any particular model, the starting method will be different, as it depends on its overall size, its general character, and other factors. While some models may operate through induction, others may run on fuel or may be powered by a capacitor.

Is there power getting to it?

What is the electrical power plug on the air compressor like? Using a power bar or power strip is not a good idea! Your air compressor should be connected to a wall outlet in order to gain the best possible power output from it. The power cord for your compressor should be at least 10 gauge, and no longer than 25 feet in length. If the cord is less than these specifications, it may actually choke off the power. There is a possibility that the power strip may have failed, in which case just remove it entirely from the equation.

In your home or garage, are you able to access the wiring breaker box or the electrical panel? You need to ensure that none of the breakers are tripped or blown inside the circuit breaker. Ideally, I recommend that you reset the fuses or reset the breakers if this is the case.

Make sure the socket that the air compressor will be plugged into actually receives power by plugging a trouble lamp into the same socket that will also be plugged into the air compressor.

Does the fuse or breaker blow again after starting?

If the failure of the compressor is the cause of the breaker or fuse blowing, then it will do so when it attempts to restart.

In order to determine if the in-line fuse needs to be replaced on your compressor, look along the wiring path, or try pushing the reset button if there is one on your compressor.

By conducting these quick checks, you can now determine that the source of the electrical problem is in the most likely case the air compressor.

In case the fuse or breakers let go when the compressor tries cranking again, it has an electrical problem. The cause of this issue could be a blown capacitor, a shorted compressor pressure switch, damage to the motor or overheating the motor as result of getting too hot. Numerous reasons can be cited.

Is there enough oil in the compressor?

Air compressors that run on oil-lubrication must be continuously refilled with oil if they are to function properly. In the event that the oil level in your air compressor is below the capacity outlined by the manufacturer, the equipment is at risk. You need to make sure that the oil level in your system is not too low, and there are no leaks under the pump.

In the event that you discover that the oil viscosity in your air compressor is not correct, you should drain and replace the oil immediately. The oil tank needs to be filled with a lubricant that has the right viscosity. While you may be able to get away with putting in the wrong compressor oil for the time being, sooner or later the additives in the oil will cause damage to the compressor pump. If you are trying to start your air compressor, but it freezes, a loud knocking noise will be heard, and as you can imagine, this is not a good thing to hear!

I had an issue with my Craftsman air compressor working once because the machine had tilted due to an uneven surface in the workshop. It’s only after I realised that the problem had been caused by this tilted base, as oil accumulated on the lower part of the machine each and every time it was refilled, which meant that there wasn’t enough getting to the important parts!

So please make sure to put your air compressor on an even surface, and if you want to stop it from moving around too much, use vibration pads!

Make sure the compressor is empty by draining the tank

Shut off the compressor by unplugging it or turning it off. It is then possible to drain the air tank by using an air tool or a blower to connect to the hose and blow all the air out. In order to drain your compressor tank (including any trapped water) completely (which you should do regularly anyway), you need to open the drain valve on your compressor tank.

It is possible to empty the compressor tank and test the pressure relief valve (PRV) at the same time by pulling the ring on the pressure relief valve (PRV) ring. You will want to wear gloves while you do this. This will ensure that the PRV is functioning effectively as it will remove all of the air from the tank. After all the tank air has been removed, press the PRV valve back into its original position. You have now successfully reset your PR Valve.

Why should the compressor tank be emptied? In that case, the unloader valve on your air compressor might not be functioning fully, so you might as well bring it to a halt and drain the tank just like it would if it were working.

It is extremely important to make sure that you completely empty the air tank in order to release any trapped air over the compressor pistons or other compression components. There is a possibility that if air was trapped in there, the motor of the air compressor may not have been able to start because of the additional load it was experiencing.

Do you have a working pressure switch?

After removing the cover, get up close and examine the pressure switch. Once you’ve done this, have someone turn the compressor on and reconnect the compressor. Are you hearing anything? Are you seeing any movement on the pressure switch?

Low pressure may trigger the pressure switch, in which case the points will move, allowing the electric motor to receive power.

I heard the click from the pressure switch – now what?

The movement of the points and the sound of a click indicate that the pressure switch is working correctly and that power is passing through the pressure switch to the motor just fine.

With a multimeter, you can check if there is current flowing across the pressure switch so that you are certain that power is flowing to the motor. Additionally, since you have a multimeter, you don’t have to get down on the floor just to check if power is flowing to and through the switch; just dump the air from the tank and power up the compressor and check it with the multimeter.

If, at this point, the motor did not start, but was now receiving power, then, it is safe to assume that it is the motor itself that is causing the problem.

Can you hear any humming noise from the motor?

If you listen closely, is the air compressor motor making any kind of noise, e.g. do you hear a humming or buzzing sound? If the answer is no, then look for a reset button or a thermal overload button near the motor, if it has one. If there is a reset button on the compressor, first ensure that it is connected to the power supply, and then push the button to reset it. Does anything happen now?

If the compressor motor starts then it could mean it was shut off due to a thermal overload as it could show it started but stopped because it overheated.

The right way to test for this is to let the pressure within the tank drop again as soon as it reaches the cut-out level and the compressor stops. The compressor can just restart if it needs to do so – the motor has cooled down sufficiently for it to be able to resume when needed.

If the compressor motor has not started again after being turned off for a long while, there could be a problem with the start capacitor or even the motor itself. If it isn’t the motor, then it could be the Unloader Valve…

Check the unloader valve to make sure it is in fact unloading

An air compressor with reciprocating pistons has a valve that allows it to reduce pressure to zero in the event of an overload. This is called the Unloader Valve. It occurs, however, only after the compressor has stopped working. If the unloader valve does not unload while the air compressor is cut out, you won’t be able to start the compressor. The loading valves on rotary screw air compressors work in much the same way as the unloading valves.

A malfunctioning unloading valve remains in either an open or closed position when it malfunctions. If the unloader valves are closed, then this can cause problems when you try to start your compressor. If you have a defective unloader valve, you may also suffer a blowdown of compressed air. An unloader valve that is stuck open, however, will cause a continuous leak of compressed air to occur.

When the compressor starts up properly after it has cooled down, check the unloader valve to see if it is operational when the compressor cuts out.

When the pressure switch transmits power to the compressor motor the next time, if the unloader valve is not operating properly, it is possible that the compressor will not start.

Are the capacitors and relays working properly?

A bad capacitor in an air compressor can cause a great deal of problems. In order to solve the problem, a hard start capacitor can assist in troubleshooting it. If you don’t have one, have a technician test it for you.

In the event that the technician determines that the compressor’s capacitor has been damaged, a replacement may be necessary.

If the problem is with the start relay, it will display symptoms similar to those of a faulty capacitor, but don’t let yourself be fooled into thinking it is the capacitor – check both!

Hopefully you will have found something in my guide that has provided the solution and your air compressor is working again! But if not, you will unfortunately have to take it to a specialist for repair. If it turns out your compressor is beyond repair, then it may be time to start shopping around for a new unit. To get a head start, check our air compressor buying guides, such as ‘Best Air Compressors for Air Tools in 2021‘ for more expert guidance on the best machines around in 2021.

Jeff Stelling

Jeff Stelling is an air compressor obsessive who has been working with compressors for over 25 years, since he was an apprentice engineer in the mid 90’s. He designed to offer technical guidance and buying advice for compressors.

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