Air Compressor Not Turning On? 8 Causes and How to Fix It

Quick answer: An air compressor not turning on is usually a power problem, a tripped thermal overload, or a tank that’s already above its cut-in pressure. Check the switch, outlet and breaker first. Then turn the switch off, let the motor cool, and press the overload reset button. If the motor hums but won’t spin, stop and read the hum section below.

Start with the boring stuff. I know it’s tempting to blame the motor, but both manuals I worked from for this guide put “not plugged in” and “breaker tripped” on the same list as a bad capacitor, and the cheap causes take two minutes to rule out.

Before you touch anything inside the shroud, unplug the compressor and bleed the tank. Makita and Campbell Hausfeld both make that the first step of any repair, and I’d treat it as non-negotiable.

What the Sound Tells You

When you flip the switch, listen for five seconds. That sound is your first branch in the decision tree.

What you hear	Most likely group of causes	Go to
Total silence	No power, tripped overload, switch off, tank above cut-in	Steps 1 to 3
A hum, but the motor won’t spin	Low voltage, trapped head pressure, stuck check valve, capacitor	Steps 4 to 7, then a technician
Starts, then stops after a while	Overheating or overload trips	Our shutting-off guide

Why It Happens

Here are the causes in the order I’d check them, quickest first.

Think of silence as electricity never reaching the windings, while a hum says current is arriving but the motor can’t overcome whatever holds the piston back, whether that’s trapped air, sagging voltage or a weak start capacitor.

1. No power at the motor. Unplugged, a dead outlet, a tripped breaker or a blown fuse.
2. The thermal overload tripped. The motor got too hot and its protector cut power.
3. The tank is above cut-in pressure. The compressor is fine. It’s waiting.
4. The switch is off or the wiring is loose. A loose connection in the pressure switch or terminal box.
5. Low voltage. Usually an extension cord, a long thin circuit, or other loads on the same breaker.
6. The unloader valve didn’t release head pressure. The motor tries to start against trapped air and can’t.
7. A stuck check valve.
8. A failed capacitor or motor.

How to Fix an Air Compressor Not Turning On

Work through these in order. Each step either fixes an air compressor not turning on or rules something out, and in practice the first three cost nothing but a few minutes.

1. Check the Power

Plug the compressor straight into a working outlet. Test that outlet with a lamp. Then check the panel.

Makita’s MAC2400 manual says to look for a blown fuse or tripped breaker, and not to replace it with a higher-rated fuse or breaker than your branch circuit is built for. It lists a 15 amp minimum circuit, prefers a breaker, and calls for time-delay fuses if your panel uses fuses. If the breaker trips again the moment you reset it, stop resetting it. Skip ahead to the technician section.

2. Reset the Thermal Overload

This is the classic answer when a compressor was running fine, stopped, and now won’t restart. Honestly, it’s the one I’d bet on.

Makita’s quick start guide gives the sequence:

1. Turn the compressor OFF.
2. Wait for the motor to cool, 60 seconds or more.
3. Press the red overload protection switch.
4. Turn the compressor back ON.

On the MAC2400, a 4.2 gallon twin-stack unit, the button sits under the shroud, to the left of the pump. Other brands put it elsewhere on the motor, so check your model’s manual for the location. Don’t press it while the motor is still hot. Give it real time to cool.

3. Check the Tank Pressure

Look at the tank gauge. Is it high? If the needle is above the cut-in pressure, the compressor won’t start, and that’s correct behavior, not a fault. Makita’s troubleshooting guide says the motor will start automatically once tank pressure drops below the pressure switch’s cut-in setting.

So if your air compressor won’t kick on right after filling, use some air from a tool or blow gun and watch the gauge fall. It should start on its own. Campbell Hausfeld warns against opening its drain valve with more than 40 PSI in the tank, so don’t use the drain to dump a full tank.

4. Get Rid of the Extension Cord

Both manuals are firm on this, and so am I. Campbell Hausfeld’s says, in capitals, not to use an extension cord and to use a longer air hose instead. Makita’s says the same and warns that low voltage can damage the motor. A long, skinny cord causes exactly the voltage drop, power loss and overheating Makita describes, and Campbell Hausfeld lists cords among the reasons a motor hums and runs slowly or not at all.

If you must use one, Makita requires a 3-wire grounded cord in good condition, sized from the gauge chart in its manual.

5. Free Up the Circuit

Campbell Hausfeld rates its 120 volt, 15 amp units for a dedicated circuit: no other appliances or lights on the same branch, a 15 amp breaker or slow-blow fuse, and no more than 40 ft of 14 gauge wire, or 70 ft of 12 gauge, between outlet and breaker. Unplug the shop heater and the radio, then try again. Don’t forget the shop lights on the same circuit.

6. Listen for the Unloader Hiss

When a compressor shuts off at full pressure, you should hear a short burst of air from the pressure switch. Campbell Hausfeld explains that this unloader valve releases pressure from the discharge tube so the motor can restart easily.

No hiss, and the motor hums but won’t turn? Trapped head pressure is a strong suspect. Makita says to bleed the line by pushing the pressure switch lever to OFF, and to replace the valve if it doesn’t open.

7. Inspect the Check Valve

The check valve is a one-way valve between the pump and the tank. Makita lists a check valve stuck open as a reason the motor won’t run, and its fix is to remove the valve and clean or replace it.

Do this only with the tank empty and the cord unplugged. Campbell Hausfeld’s manual repeats the warning beside every check valve entry: never take it apart with air pressure in the tank. Makita’s service steps say the valve disc should move freely, with the spring holding it in the upper, closed position, and that the valve can be cleaned with a suitable solvent.

8. Leave Capacitors and Motors to a Pro

If you’ve worked through steps 1 to 7 and still get a hum, or nothing, the remaining suspects are electrical parts inside the motor. Campbell Hausfeld lists defective capacitors and a defective motor. Makita routes both to an authorized service center rather than giving owner instructions. I’d follow that advice.

How to Reset an Air Compressor

When you ask how to reset an air compressor, you almost always mean the thermal overload button in step 2. That’s the reset both manuals describe, and it’s the one most likely to bring a cooled-down motor back.

The pressure switch is a different story. Neither manual I used describes a reset button on the pressure switch. Turning the switch to OFF and back to AUTO or ON is the closest thing, and on Makita’s design, moving the lever to OFF also dumps trapped head pressure through the unloader. I’d leave the cut-in and cut-out settings alone. They’re factory set, and the safety valve is set just above cut-out.

When to Call a Technician

Stop and get help if:

• The motor hums but never spins after you’ve ruled out low voltage and the unloader. Campbell Hausfeld lists defective capacitors and a defective motor as causes, and Makita sends capacitor problems to an authorized service center.
• The breaker trips the instant it starts, every time, on a dedicated circuit.
• Wiring looks burned inside the pressure switch or terminal box.
• You suspect the voltage. Campbell Hausfeld says a qualified electrician should check undersized or overly long supply wiring.

My take: a hum with no rotation is the line I’d draw for DIY work on an air compressor not turning on. Below that line it’s power and patience. Above it, it’s parts and wiring.

If yours starts but won’t stay running, see air compressor keeps shutting off. If it runs but sounds rough, read why is my air compressor so loud. More fixes live in our shop equipment section.

Frequently Asked Questions

Why Won’t My Air Compressor Kick On?

If the tank gauge reads high, the tank is still above cut-in pressure, so the switch is doing its job. Use some air and it should start. If the tank is low and it still won’t start, check power and the overload reset.

Where Is the Reset Button on an Air Compressor?

It’s usually a red button on the motor. On Makita’s MAC2400, it’s under the shroud to the left of the pump. Check your manual for your model’s location.

How Long Should I Wait Before Resetting the Thermal Overload?

Makita’s quick start guide says 60 seconds or more. If it trips again quickly, look for low voltage, an extension cord or poor ventilation. Makita also recommends running its compressors at no more than a 50% duty cycle.

Can an Extension Cord Stop an Air Compressor from Starting?

Yes. Campbell Hausfeld lists extension cords as a cause of a motor that hums and runs slowly or not at all. Use a longer air hose instead.

Why Is My Air Compressor Not Turning On but Humming?

Low voltage, a failed unloader valve, a stuck check valve or a bad capacitor. Rule out the cord and circuit first, then the unloader hiss, then call for service.

Last updated: November 10, 2026. Sources: Makita MAC2400 instruction manual (PDF), Makita compressor quick start guide (PDF) and Campbell Hausfeld CE1000/XC302100 manual (PDF).