thermal switch cutting in

[RaceDiagnostics]

Hi, I bought this compressor on ebay about 4 years ago for £40, I have no history of how old it is or how many hours are on it. Recently the thermal switch has been cutting in before it gets up to pressure, say about 7 bar, pushing the thermal cut out back in allows it to keep going normally.

Any ideas on how to fix it? Is it fixable?

 

[eil]

Inlet air filter clean, oil ok, checked all electrical connections tight, check microfarad of capacitor, put clamp on amp meter on to check current draw.

 

[rtbcomp]

Could even be a faulty thermal cut-out.

 

[addjunkie]

Looks like a generic chinese compressor all parts are cheaply available on the bay of evil

 

[Jetex]

If the compressor seems like it is running normally then it could be as already mentioned a faulty cut out switch. The switch on this looks like a resettable fuse type and should have a current rating stamped on it. Whip that plastic cover off and have a look. If you have a current clamp it is worth to measure the current of the motor to see if it is drawing too much current, in case of a bad bearing or tight compressor pump. I have a similar small compressor like that but mine does not have a thermal cut out switch.

 

[frank horton]

disconect the thermal cut out, then try it, not straying far just in case.....then as I'd guess it'd be OK, then just forget it....remember it's fused anyway......
always had trouble with these thermal cut outs......
by my experience if the T/cut/0 trips twice on anything Chinese I just by-pass it.....Frank

 

[RaceDiagnostics]

Thanks guys, a few thing to look into.

 

[RaceDiagnostics]

Something weird just happened, I had used the compressor yesterday morning, it tripped by the time it got to about 7bar on the first cycle, I then used it till most of the air was out and just left it and didn't turn it off. Just a minute ago I heard it start up and go through a cycle.

Do these thermal cut out reset themselves automatically? 24 hours to reset sounds like a faulty thermal switch.

 

[carbon]

Not usually, they have to be manually reset

 

[Turbo]

Do these thermal cut out reset themselves automatically? 24 hours to reset sounds like a faulty thermal switch.

The thermal cutout on one of my small compressors will cut out if I'm using a die grinder or sander for too long due to the compressor getting too hot. As soon as it cools down again it resets itself.

Is the compressor taking longer than usual to fill up? If so it could be exceeding its duty cycle & getting too hot. There could be a problem with the pump or the non return valve.

Another thing to look at is the capacitor as these can fail. A failing one can cause the motor to run too hot. You can do a basic test on them with a multi meter but you need a capacitance tester for a proper test. They're fairly cheap on ebay so it mught be worth trying a new one.

 

[RaceDiagnostics]

Here is a video of the compressor, the fault got a lot worse lately.

From cold the compressor will run for a few seconds the trip out, pushing the thermal cut out will some times work, sometimes not.

Here is a video, it cuts out again at 20 seconds.

I'm guessing this might be an over current switch rather than a thermal switch.

I measured the current with a clamp at the switch and it was ~7A but the switch also says 7A on it.

Maybe the compressor is taking too much current?

 

[rtbcomp]

It's called a thermal switch because there is an element that heats up when too much current is drawn and trips the switch. It's not because it senses a high temperature. There are switches that sense temperature and/or current but not in this case.

It doesn't restart immediately because it needs a few seconds to cool down to allow you to reset it.

It's not unknown for these switches to become too sensitive, so try changing it as a first step.