Hitachi EC12 Compressor Won't Cut in, trips breaker

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Old 07-14-14, 03:26 PM
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Hitachi EC12 Compressor Won't Cut in, trips breaker

I have an old Hitachi EC 12 compressor that seems to run okay when the compressor first comes on. It builds pressure and seems to be holding it okay, but I might need to double check that.

Once it reaches the maximum pressure and cuts out, it doesn't properly cut in again. When the pressure reaches the cut-in pressure, I can here the compressor hum a little and try to start the motor but it can't start and the breaker trips after a few seconds.

I've seen that this could be the capacitors on the motor, is this the most likely cause of something like this? I have a new pressure switch on the way because at first I thought it was this but then someone suggested it could be those caps. I'm planning to pull them out and check them when I have a little time but I'm looking for other suggestions in case they don't seem to be the problem.

Thanks!
 
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Old 07-14-14, 08:32 PM
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Welcome to the forums.

That unit lists as drawing 14.5A so that means it needs to be used on a 20A circuit. Most compressors use a pressure relief valve built into the pressure switch that relieves the pressure that's inside the compressor cylinders so the pump doesn't start under load. I can't tell from the parts list if yours has that feature.


Hitachi power tools/PDF/All/EC12_E4_BD.pdf
 
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Old 07-14-14, 10:28 PM
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To be honest, I'm not sure either. Any way to tell? Is that the same as the unloader valve?
 
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Old 07-15-14, 09:38 AM
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I checked out the caps. Both measure around 39 uF, 39.1 and 39.3 to be exact. I also checked them by measuring the resistance and they both looked good as far as that went. They slowing increased in resistance the entire time I was measuring. So, they both seem okay, which is good because the only replacements that I can find were 35-40 dollars a piece. Getting dangerously close to better-off-buying-a-new-compressor territory.

So, for now, I'll test the check valve and probably replace the pressure switch.
 
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Old 07-15-14, 09:56 AM
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It's not going to be a "pressure switch" problem but it could be an unloader problem that is attached to the pressure switch. When your compressor reaches cut out pressure - the motor will stop and you should hear air coming out of the unloader valve for usually around 10-25 seconds.
 
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Old 07-15-14, 11:36 AM
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The unloader is something different than the pressure relief valve that you were talking about, right?

How can I tell the difference?

When the motor stops I do think I recall hearing a burst of air but I'm not certain of the duration. I'm pretty sure it's stops after a short time, though. I'll check that. If it's the unloader valve, does it just continue to blow air out until the pressure drops entirely?
 
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Old 07-15-14, 06:39 PM
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Did some research. I know where these two valves are on my compressor now. I'm planning on checking out the check valve and hopefully replacing the pressure switch when it arrives tomorrow, if the check valve seems fine.
 
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Old 07-19-14, 12:09 PM
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Had some time to check it out again today and I'm thinking it's the check valve.

I let the compressor run until it was full and it cut out. What I was surprised about was that I didn't hear the burst of air that I had heard previously when the motor would shut off. I'm not sure if that necessarily means anything. From there, I let it sit for a minute just to see if it lost any pressure at that point which it did not.

So, now that I felt okay that the tanks were holding air, I went and opened up the line that runs from the head of the motor to the check valve. For a good valve, I was expecting a quick burst of air and then nothing. Instead, I got a sudden, constant rush of air out of the tank. The tank continued to lose pressure until it reached the cut-in pressure and at that point the motor cut-in, no problem. So, it doesn't sound like it's the pressure switch and instead it's the check valve. Is there a good way to try to clean it to see if that will help? Is there anything I can look for with it to see if it's salvageable or just needs to be completely replaced. I don't mind getting a new valve itself, it's just the wait for the part to arrive.

Also, should I worry about the fact that I didn't hear the burst of air come when the motor cut out. If I understand correctly that should come from the unloader valve. Is there any chance that means there's a problem with the unloader valve or somewhere else, maybe, or does that just not always occur?

Thanks for the advice!
 
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Old 08-25-14, 01:25 PM
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I finally had a chance to fire the compressor back up after replacing the check valve. It seems like that was the problem all along. when it dropped below the correct pressure, it cut back in as expected.

Thanks for the help on getting this fixed!
 
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