air compressor issues

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Old 04-11-09, 06:40 AM
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air compressor issues

I have a craftsman air compressor 5.5hp 30 gal. Model No. 919.165050. It draws 15 amps. The compressor is wired to a 20amp outlet with 12/2 wire that is 3 feet from the breaker panel and blows the breaker 6out of 10 times on start up. Im wondering what the problem is. Motor runs fine once started...could it be starting or run capacitor? I have tried to find the company who makes the motor (sears wont sell parts just the whole motor) if found there site once then lost the link Im not sure what the issue is...Please help thanks, Jason
 
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Old 04-11-09, 07:40 AM
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There may be nothing wrong with your compressor. When a motor starts it can draw up to 3 times the running current. I have seen many a compressor trip breakers on start up or even seen the motor stall. You could try replacing the breaker to see if that changes anything. Or if it is not on a dedicated circuit install a 30 amp circuit for it.
 
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Old 04-11-09, 08:10 AM
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Can't think of the correct terminology but isn't there a valve to release head pressure when starting? See if that valve is working.
 
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Old 04-11-09, 08:24 AM
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Pressure release valve...you should hear it hiss as it stops running after hitting the upper limit cutout.
 
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Old 04-11-09, 08:36 AM
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This is info I found at another site, Looks like some good stuff here.


Most compressors cannot start with a full head of pressure. They should have a start unloader of some sort and a check valve between the compressor and the holding tank. The unloader relieves the pressure off the pistons and the check valve only allows air to flow in one direction, towards the tank.

When the compressor stops, the unloader will open allowing the air pressure to drop on the pistons and the check valve will close keeping the tank air from escaping through the unloader.

If the check valve is stuck open, then the compressor is trying to start with a full head of air. You may also note that the air pressure in the tank may be going down faster then normal when not in use.

Follow the lines from the compressor to the tank and you should be able to locate these items. Be careful as parts under pressure can and will blow off with great force even though you think the pressure is low. If you hear any air escaping while removing parts, wait until the sound stops and then remove slowly.

If this is of no help, you may have a bad motor that will not develop enough starting torque to over come starting pressure but runs fine once it gets going.

Check your manual if you have it. Sears/Craftsman are good about having all the information packed with the unit including a parts list.

Again, this is general and may not apply to you unit.

PS. I am adding this after checking my Craftsman compressor. The compressor may have a bad discharge reed valve.

There are 2 types of reed valves for each cylinder. As the piston goes down, the intake reed valve opens to let air into the cylinder. As the piston goes up and compresses the air, the discharge reed valve opens when the pressure is equal to the tank pressure.

If this reed valve is damaged, it will allow tank pressure back into the cylinder. This would act the same as a bad check valve.
 
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Old 04-11-09, 08:49 AM
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Yeah...unloader is a better term, but Sears calls it a PRV in the manual. BTW, the manual they have online is pretty useless. No spec's, very generic.

You could just have an old breaker as well.

Oh, and I think this is a 120VAC unit, so I don't think you can have a 30 amp line...can you? Isn't a residential 120 circuit limited to 20A max? No expert here, just seems like I read that somewhere.
 
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Old 04-11-09, 10:37 AM
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You can have a 30 amp on 120 volts, but it would require rewiring with 10-2 wg. I would opt, since it is a Craftsman to switch it to 240 volts (provided it has that option). It requires changing two jumpers in the peckerhead and rewiring with a new 240 volt plug, receptacle and you can keep your 12-2 wiring and change the breaker. You will realize less bogging at startup.
 
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Old 04-11-09, 10:48 AM
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Originally Posted by Gunguy45 View Post
Oh, and I think this is a 120VAC unit, so I don't think you can have a 30 amp line...can you? Isn't a residential 120 circuit limited to 20A max? No expert here, just seems like I read that somewhere.
I don't recall ever seeing anything that limits residential to 20 amps max on a dedicated line. The receptacle would have to be a 30 amp and would the cord would also have to be changed.

Speaking of the cord, take a look at the existing cord. Maybe it is a little light and the voltage is dropping a little too much. Although, I find this a little hard to believe since it is so close to the panel.

Also, you said the compressor of 5.5HP. convert that to watts and you get about 4100 watts?!? At 120 volt that would be 32.8 amps and at 240 volts it would be 17 amps. I know motor manufactures seam to fudge on their HP ratings but I guess I'm wondering if this is already a 240 volt compressor.
 
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Old 04-11-09, 10:57 AM
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Ok, maybe I was thinking of standard receptacles? Even if you put 3 or 4 on the line?
I can see there wouldn't be any problem with a correctly wired dedicated outlet and upgraded cord, wiring and breaker. It's probably the allergy meds fogging my brain. Anyway...no matter.

Also, according to the not so helpful manual online, no mention of being able to switch to 240. It said it only needed a 15A 120, unless problems were noted due to other loads on the same circuit, then they recommended upgrading to a 20A.
 
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Old 04-11-09, 11:34 AM
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Hmm ill have to look into that valve. Where exactly is it and how do i know how to check it. Thanks for the replies everyone
 
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Old 04-11-09, 12:04 PM
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If the unloader/pressure release is working, you will hear a hiss or "PFFFT" when the motor cuts out at upper limit. Many of them also have a manual ring or chain you can pull. Let me link to your manual (if I can find the valve on it).

Parts diagram.....http://www.searspartsdirect.com/part...ponents%20list

Manual....http://www.managemyhome.com/mmh/lis_...M/L0803438.pdf

Hope both the links work OK, may need to register at manage my home.

I think #22 may be the release, though they say its the safety valve. In the manual it says it's mounted on the side of the regulator, and thats the only thing I see there. As I said, the manual isn't that great.
 
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Old 04-11-09, 12:59 PM
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i just went through and checked all the electrical connections. It will turn on initially with no problem now. However as i use it and it senses the pressure drop and attemps to kick back on it blows the breaker. I have a brand new 30 amp breaker is it safe to wire it to it? I would run new 10/2 wire. The only thing is what about the outlet(its only a 20a) and what about the compressor wiring itself?

I discovered that the pressure release is letting off pressure when it shuts down so that rules that out. I can rewire this bad boy in 30 minutes, just not sure if its ok to do so?
 
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Old 04-11-09, 04:08 PM
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There are few spots that you can use larger breaker one area I know for sure is Compressor motors you can use larger breaker if the situation called for however as other readers give you good points they are right on the target check the unloader valve that is most common curpit.

It should not have any sluge or gunk in the valve to prevent operating correct { a instering twist check the oil in the compressor most are pretty picky to use low ash or compressor oil a plain jane motor oil can gunk up the valves if not carefull with it }

As I mention about using the larger breaker that is in the NEC art 430 and 440 I will just keep that to the last resort after other items checked out good first to advoid any issue along the way.

I just replace the unloader valve on my monster compressor last fall { 15 hp size } and it very easy to get into there as most compessor useally right on the head and check the reed valves as well but let me give you a serious head up with reed valves do not bend them they don't take much to get them out of wack if not carefull { it the same sisuation if you work on two temp {cycle } gas motors reedvalves }

Merci,Marc
 
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Old 04-12-09, 07:42 AM
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The valve is working fine I spent about 30 minutes or so checking it and it does what its supposed to.

I really just wanna up the breaker and call it done. I just need to know if its ok to do so?
 
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Old 04-12-09, 08:05 AM
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There are some special situations that allow you to use a larger breakers on smaller wires with motors. Here is a calculator if you want to go that route: electrician2.com Motor Circuit calculator

However, just to be safe, just change the breaker. You will have to up the wire to #10 copper as well. You will also have to change the receptacle and the cord cap to 30 amp on the compressor. Also, if the cord is light you should also change to a heavier cord. (#12 or #10)
 
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Old 04-12-09, 12:45 PM
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Some case you can get what we called " high mangtic " breaker that some case useally can handle high inrush current like electric motor or transfomer some case HID/Flourscent ballast.

Those breaker useally found in electrical supply centre some big box store can order it for ya { some cost the same as reguar breaker some not }

Again myself and Toyln mention that one of few area have specal permission to increase the OCPD size and they are only restricted to motor or hemispere compressor motors as it stated in art 430 and 440.

For the cord just do as Toyln suggest change to heveier cord that useally take care that issue and change the plug as well.

Merci,Marc
 
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Old 04-12-09, 04:17 PM
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The cord i have now is pretty heavy, how about the pressure switch and the wiring for the motor is that ok to up the breaker on?
 
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Old 04-12-09, 05:06 PM
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Could you kindly post ALL of the information from the motor's data plate? A 5.5 hp motor on 120 volts with an FLA [full load amperage] of 15 amps does not sound right. Maybe you meant to type .5 hp?
 
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Old 04-12-09, 06:34 PM
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I did mention that before :
Also, you said the compressor of 5.5HP. convert that to watts and you get about 4100 watts?!? At 120 volt that would be 32.8 amps and at 240 volts it would be 17 amps. I know motor manufactures seam to fudge on their HP ratings but I guess I'm wondering if this is already a 240 volt compressor.
but nobody seamed too concerned about it.

If the cord is pretty heavy (#14 or #12 it should be stamped on the outside) you should be fine. Either way the compressor will still draw the same amount of current weather it is on a 20 amp breaker or 30 amp. The cord should have been sized correctly by the manufacture. I only suggested it in case the manufacture put an 18ga cord on the compressor.
 
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