Air Compressor Cycles On and Off

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The problem is that the air compressor cycles on and off.

Your air compressor tank pressure has fallen to the normal cut in pressure setting, the pressure switch has tripped to ON and power is flowing to the motor circuit, the motor starts, the pump starts pumping, then before the tank pressure reaches the normal cut out pressure, the compressor motor stops, then starts, then stops and so on.

There are a couple of quick checks you can do at this point to try and diagnose the problem.

Air Compressor Cycles On and Off – 1st check

The easiest one is to pull the cover off the compressor pressure switch, assuming you have access to it on your model of air compressor, and watch what happens inside the pressure switch box as the compressor cycles.

Please be careful. Inside the pressure switch container there are live terminals.

Inside a typical air compressor pressure switch
Inside a typical air compressor pressure switch

Before you start, shut off the air compressor, and drain the tank down to zero. That will ensure that the pressure switch will immediately switch on when you start or plug in your air compressor.

Plug in or start your air compressor, and try to be watching inside the pressure switch as you do so. Can you see the terminals (points) inside the pressure switch? They  should move when the switch trips to on, power should then flow to the motor circuit, and the compressor should start.

Continue watching and if your air compressor cycles on and off before the tank pressure reaches normal cut out, and if you can see the points opening and closing while the air compressor turns on and off, then odds are pretty good that it is the pressure switch itself that is failing. The symptom suggests that it is possibly a diaphragm failure inside the switch, but regardless of the why of it not working,  if this were our air compressor, it would be time for a new pressure switch.

Fix The Pressure Switch?

It is possible to fix a compressor pressure switch. It is our experience however that with the relatively low cost of a replacement switch, that it is difficult if not impossible to get parts for many pressure switches,  that the learning curve to understand how to disassemble them so that the pressure switch can be reassembled is so high, that the real lowest overall cost to fix the pressure switch makes buying a replacement your best bet.

Inside a compressor pressure switch showing terminal connections
Inside a compressor pressure switch showing terminal connections

2nd Check

You cannot see the pressure switch points when you look inside your pressure switch housing? If you cannot see the points inside the pressure switch housing, then it’s time for a multi-meter or an electrical device to be used, one that allows you to determine if power is present in a wire or not.

With the multi-meter you can actually do two checks.

Probe the line or supply side of the pressure switch terminals where the feed from the wall plug terminates and ensure that power is present. Allow the compressor to cycle on and off if it will do so. If the power coming into the supply side of the switch is cycling on and off as well, then your problem is the supply power to the air compressor, not with the air compressor at all. Your system has a problem with the circuit you have bringing power to the plug or down to the compressor pressure switch from the breaker or fuse in the panel, or in the plug socket, perhaps.

Assuming your power supply to the supply or line side of the pressure switch is constant, now probe on the motor or circuit side terminal inside the pressure switch and watch the multi-meter as the compressor runs. If the compressor cycles off and then on, and the power on the circuit / motor side of the pressure switch is cycling off and on as well, then it’s pretty certain you have a failing compressor pressure switch.

Why Else Air Compressor Short Cycles?

If you have determined that the power supply to the switch is good, and the switch stays closed with power passing through it to the motor circuit, and the compressor motor is cycling on and off, the next check with be the motor run capacitor, the start capacitor may have failed, or the motor itself has a problem.

More on resolving the compressor capacitor or other compressor motor issues can be found on other pages on this website.

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Essam
Essam
June 12, 2016 6:45 am

I have Kaeser M70 with 900 hrs. used . Now the machine start and run for seconds then off . What possible causes ?

Fix My Compressor Moderator
Fix My Compressor Moderator
Reply to  Essam
June 12, 2016 9:57 am

The Kaeser M70 is a mobile, tow-able compressor, with a rotary screw pump and gas or diesel engine. The unloader in a continuous run rotary screw compressor allows the engine to run at a lower RPM when there is no demand for air. When the demand for air grows the throttle / unloader control revs up the engine and the compressor is again pumping air. That your M-70 starts and then shuts down points to the unloader / throttle as a possible issue. We would suggest that it’s a maintenance issue, and that you should, if you have not got one, contact Kaeser – productinfo@kaeser.com – and acquire a manual.