Air Compressor Will Not Start!

The air compressor will not start? What do you do now? Read on for some tips and ideas about why the air compressor will not start, and what you can do about it!

If you wish, you can use the comment form below to ask for more information. Please be sure to identify the make and model / part number of the air compressor in question, and also as much info as possible. For example:

Is this a new problem for your compressor?

How old is it the compressor and what’s the use been… every day, once a week, monthly?

Is there power at the socket into which the compressor is plugged?

Is the tank empty of air when you have tried to start the compressor?

Is it making any sound at all when you are trying to start it?

In order for folks to help with an air compressor that won’t start by answering a question in the comment box below, more information is much better than less info, so please provide as much information as you can if you are asking for help.

Having said that, here are some ideas that you can check right away.

Empty the compressor tank.

Seems like a silly thing to do first, but more than one compressor that was thought to not start, simply did not start because the air pressure in the tank was high enough that the compressor pressure switch would stay off.

By emptying the tank the pressure will drop below the cut-in pressure of the pressure switch, and if that’s all that the issue was, the compressor will start.

Dumping all the tank air also ensures that there is no air trapped over the compressor piston which, may, overload the motor and prevent the compressor from starting.

Power at the wall socket?

Is there power to the wall socket, and also to the compressor?

If you have a simple non-contact voltage tester for AC power that will help. If you are comfortable with using, and have a, multi-meter, that’s even better.

Check to be sure that there’s power at the socket by using one of the tools noted above, or plug a lamp into it. Pick one that’s on, just unplug it, and then, when you plug it into the wall socket, the light should come on.

Or, open the panel / breaker / fuse box and be sure that there no blown circuit breaker or fuses.

No power at the wall socket could be the only reason the air compressor is not starting. Rectify that by replacing a fuse or breaker in the panel, and then check the socket again to be sure that power is actually there.

If it was a breaker or fuse in the panels that was blown, you might also wonder what it was on this same power circuit that caused the breaker or fuse to blow in the first place? You may have to correct that too!

Next, if there is power at the wall socket, then is there power to the air compressor?

Power to the compressor?

Just because there is power at the socket into which the compressor power cord is plugged doesn’t necessarily mean that power is getting to the compressor. Wires do break inside power cords.

With the compressor plugged in, and the cover off of the compressor or pressure switch, depending on what type of compressor you are troubleshooting, find where the power cord enters the compressor. Use the poke probe or multi-meter to test for voltage there.

If the voltage tester lights up, yup. you’ve got power to the compressor.

But now, how about the pressure switch?

Is power crossing the pressure switch?

One of the reasons we empty the tank to test why an air compressor will not start is that now the pressure switch should have tripped to passing. That means that power that has arrived at the LINE side of the switch, should now be crossing the switch and be on the MOTOR or LOAD side of the switch.

Use your meter of choice, with care as always, and determine if power is on the MOTOR or LOAD side of the switch.

With the tank empty, and power on the LINE side, power should be reaching the MOTOR or LOAD side of the switch. If it is not, there is something out of whack with the compressor pressure switch, and it’s time to replace it.

Power goes to an ON/OFF switch first!

Some air compressors have an ON/OFF switch. It may be on the pressure switch – a toggle or lever – or the ON/OFF switch may be elsewhere on the compressor housing.

Typically, power will travel from the power cord to the ON/OFF switch before it reaches the pressure switch.

To be sure that it’s not the switch that’s the problem, follow the same drill. Check to be sure that power is at the supply side of the ON/OFF switch, and then, with the switch turned on, make sure power has crossed the switch.

If it has not, it’s time to replace the compressor ON/OFF switch. If that switch is part of the pressure switch assembly, you’ll likely have to replace the pressure switch.

Power is crossing all compressor switches!

From the pressure switch, the power flows to the motor circuit.

If you have not already done so, remove all covers from the compressor so you can see what’s what.

Follow the power wire from the pressure switch to where it arrives at the air compressor motor.

Small air compressors really shake, rattle and roll when they are running, so don’t be surprised if you find that a wire has come loose. Check all connections, and remember that you are working with a live wire, so before touching anything, cut the power off.

If all wires are secure, it’s time to look at the motor itself.

Look for a compressor motor capacitor.

OK, I can hear you saying, what’s a compressor motor capacitor?

Odds are pretty good the compressor motor will have one, or maybe two, capacitors. If two, one’s for a start capacitor, and the other is the run capacitor.

Be very careful as capacitors are quick release batteries, and if you ground yourself while touching a lead, you’ll be sure you’ve been swatted by a lightening strike, if you survive… really, be careful!

Look very carefully at the connections to the capacitor(s) and from them to the motor. I’ve heard lots of tales about how vibration and corrosion have essentially cut the power at these connections.

OK, the thing is, if power is getting to the capacitor/s and power is not getting out of the capacitor to the motor, then it’s a pretty safe bet that you’ve had a compressor motor capacitor failure, which isn’t all that uncommon.

Go to this page and scroll to the bottom to see a video about how to test your compressor motor capacitor.

Compressor still won’t start?

If the compressor motor capacitors check out as good, and their connection to the motor is secure, then that defaults to it being a problem with the motor itself.

If you’re getting a whiff of burnt smell, that might have been a failed capacitor, but since they check out, that burnt smell may indicate a short in the wiring inside the motor.

It’s time to get the motor tested. That means either carting the whole compressor, or removing the motor and just taking that, to an electric motor repair shop for a motor test.

If the results of the motor test suggest that the compressor motor is fine too… well, leave a comment here with details. We all would like to read about that.