Compressor cutting out mid cycle

[Jim mcgrath]

My four horsepower Clarke compressor is stopping before it has completed its cycle by the built in trip switch popping out. It stops without unloading the air in the pipe although if I push the button down on the pressure switch it releases the air.
I changed the pressure switch but without improvement. I unscrewed the pipe which attaches to the check valve and there was no leaking air. I checked both capacitors with the multimeter and they showed a normal reading. I took the front of the motor to check the clutch that moves back and forth, It seems ok. That’s the limit of my troubleshooting knowledge.
Has anyone any ideas what else I might check.

 

[carbon]

What pressure does it get to? How much current is the motor drawing when this happens?

 

[dave h 2]

The pressure switch trips the unloader, the thermal safety switch does not.
The only time I had a thermal trip was a 3/4hp motor pulling twice the rated amps on the motor plate.
is the motor casing very hot? If it isn't the trip may be bad

 

[tom2207]

quick test , does the compressor smell hot ?

 

[Jim mcgrath]

I was going to test current tomorrow with a clamp meter. I’am not sure of the best wire to clamp it around? Could you give me an idea?
Not sure of the pressure it gets to but it’s well short of the maximum capacity.
The motor casing isn’t hot, it really doesn’t run long enough for it to get hot.
No smell of heat or burning or anything like that.

 

[Seadog]

You need to clamp it around a single conductor not a multicore cable.

 

[brightspark]

you can clamp it on to either the live or neutral which ever is easiest to get on feeding the motor

 

[dave h 2]

When mine cooked the thermal cutout the motor casing was too hot to touch so 60C+

 

[Turbo]

Is it only doing this when the compressor is starting from cold?

Drain the air completely and run the compressor with the drain tap open for 5 minutes to warm the pump.

Close the tap and see if it fills without tripping the thermal cutout. If it works the oil in the pump is too thick in cold weather. Swap to a good multigrade 10w30.

checked both capacitors with the multimeter and they showed a normal reading.

What do you mean a normal reading? You need to measure the capacitance, most multimeters can't do this.

Those thermal button cutouts do get tired, I've had to change them before.

But measuring the running amps will be the first step.

 

[bourbon]

Common at this time of year, especially if the compressor is stored outside. is the compressor drained? with no water at all? Then, all of the above.

 

[Bornfree]

Sounds like the run capacitor is low

 

[Jim mcgrath]

My first thought was the cold weather too. The start capacitor is rated at 200 microfarads but is giving a reading of 287 microfarads. At first I thought this was ok because it was a higher number but this seems a long way out. I’ve ordered one from eBay. The run capacitor was showing the correct reading.
I tried measuring the current with a clamp meter and It read 5.5 amps but this can’t be right. I don’t know much about it but I think it should draw higher amps than that.
I drain the compressor regularly and there is no water in it. As far as the pump being cold, You could be right, however the first day this happened it ran for a while and cut out and I restarted it. This restarting and running for a while and then cutting out continued for a good few times so I think it must have warmed up during all that.

I must be doing something wrong when trying to measure the current with the clamp meter, so if anyone has any tips on that it would be appreciated.

 

[carbon]

With a clamp meter you usually just clamp around one cable. The easiest place is usually inside the box on the motor. At low pressure the current draw may not be above 10amps. Check on the motor plate for the rated current, it shouldn't exceed that value at full load.
The start capacitor being at 287 uf should be fine, the value may be on the motor plate as well. I don't see to many motors with separate start capacitors but usually motor plates show start capacitor 200-300 uf for example

 

[Seadog]

The capacitors are usually rated at +/- 20%, so it's not too far out of value.

 

[Turbo]

Did you try measuring the voltage under load?
You could have a bad connection somewhere or too light a supply causing voltage drop.

 

[Jim mcgrath]

I drained all the air from the tank and then turned it on to see how far it would fill before the overload popped. This is where it got to.

 

[angellonewolf]

8 bar is where mine gets to but a smaller tank but its pressure so what was it running at before and when you swaped the new switch did you set it up for pressure ?

ops sorry its a trip switch did see that

did you look at the oil ?

 

[Jim mcgrath]

I fitted a new pressure switch but I didn’t make any adjustments to it. The first time I ran the compressor after fitting the new pressure switch, it finished the cycle and cut out on the red line you see on the dial. The overload didn’t pop and it vented the air from the pipe, so I thought I don’t need to do anything to that, but it has popped the overload every time since.
Do you think the oil might need changing? I thought I could see the oil level through the little sight glass although now that you have pointed it out, it could be a high tide mark I am seeing.

8 bar is where mine gets to but a smaller tank but its pressure so what was it running at before and when you swaped the new switch did you set it up for pressure ?

ops sorry its a trip switch did see that

did you look at the oil ?

 

[angellonewolf]

it was said about ealier its worth a cheak might even be worth changing for the earlier

have you taken out the drain plug and (ever regularly drained it ? if not poke some thing up in the hole after removing it the one at work never got drained untill i started beware there will be a lot of pressure there if its full )

 

[Jim mcgrath]

I will change the oil tomorrow as it’s time it was done anyway. When I open the drain there’s always water comes out but I will take the plug out completely to make sure that it is letting all the water out.