67847 compressor won't built pressure?

by Eric
(Reading, PA)

Compressor parts - http://www.about-air-compressors.com

Compressor parts - http://www.about-air-compressors.com

I have an older version of the central pneumatic 67847. It's a 21 gallon 3hp compressor.


I bought it used, and on the way home it rolled over. The oil fill cap came unscrewed and I found 2 parts laying on the ground. A little check ball about 1/4 of an inch and a little disc about 3/4 of an inch across with 3 tiny holes in it.

The compressor will not build pressure over 60 psi. Is it related to this check ball / disc? They had oil on them so I think they came out of the oil fill spout. I may have also lost more parts that I didn't see.

The compressor is not turning off at 60psi it just runs forever. With the switch off I do not hear any hissing from inside the compressor just a tiny hiss on the hose.
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Bill says...

Eric, the items in the photo look like the venting for the oil fill cap. The check ball/disc may be just to allow air into the sump but to keep crap out. There is often a filter media in the cap to do that... you may have a more advanced cap.

No, I don't think the parts have to do with the fact that your air compressor will not build pressure past a certain point.

I have written, as have many, many visitors, about this issue.

Step one for me is to empty the air compressor, pull the intake filter, start the compressor and see if air is being pulled in or not. If air is being pulled in strongly, that suggests that the intake valve is fine.

On the troubleshooting page "compressor will not build pressure" are more checks. Please have a look at that page, review what you can, and post your findings here as a comment if you still need help after that.

Cheers,

Bill

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Dec 11, 2014
Valve?
by: Bill

Yes, possibly valves, possibly piston seals, but definitely not the regulator, which has absolutely no bearing on the tank pressure.

If the problem is no air out of the hose, then yes, the regulator could be the problem.

Or, it could be that someone has parked their car tire on the hose, and effectively blocked the air flow, as happened to another person who commented on this site.

Bill

Dec 11, 2014
sounds like valve assy in the cyl head
by: Anonymous

The most common issues with a compressor not building pressure up is tank or lines leaking, worn out piston ring or cylinder walls scored, broken reed valve in cylinder head assembly ( air blowing back out the intake), wrong regulator adjustment. Clogged or restricted air filter, no oil in compressor (oil type), but of all of these the most common is scored cylinder/ bad ring or broken valve in cylinder head. Removing the air filter assy and checking intake suction is a good place to start. you can remove the output line coming out of the compressor and see if there is pressure there if so then you may have a tank or regulator issue. If say it maxes out at around 40 psi chances are worn out cylinder or bad valves also. Good luck!

Oct 28, 2014
Pressure
by: Bill

I cannot take a look at your compressor as you don't indicate the model.

As a comment here, tell me what the pressure reading is on the tank gauge, and what is the regulator (see regulator gauge) pressure set at?

Bill

Oct 28, 2014
need help
by: Anonymous

I have a 100 psi 3 gal central pneumatic hot dog compressor

it comes on but when I squeeze the air release I don't hear the air coming out I don't see any pressure getting high wats up?

Oct 20, 2011
gasket
by: Eric

It's also blowing air back through the oil fill. I read somewhere on here that replacing the head gasket with automotice head gasket material might work. If air is blowing back out the intake and back through the oil fill would replacing the head gasket be likely to fix it?

Thanks

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Air blowing out the intake is indicative of the intake valve failing. Air blowing out the oil fill tube suggests the piston seals have failed.

Oct 20, 2011
:(
by: Eric

I just tested and it IS blowing air back through the intake starting around 38psi.... seems a real shame because the motor is running like a champ...

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Compressor keeps shutting off?

by Mike
(Chippewa Falls, WI)

Air Compressor, Cast Iron Vertical, 2.5 Horsepower, 21 Gallon, 125 PSI  (photo: www.harborfreight.com)

Air Compressor, Cast Iron Vertical, 2.5 Horsepower, 21 Gallon, 125 PSI (photo: www.harborfreight.com)

I have a Central Pneumatic 21gal compressor, bought new in fall used it a couple times.

It would never turn over in winter and now that it's warm out I tried it this weekend and it would run for 2 sec then shut off, sometimes it would run 15 sec and shut off, keeps popping the circuit breaker.

I drained the tank completely so there was no pumping resistance and same thing happened. Not sure if its the breaker or what?
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Mike, the symptoms you wrote suggest that your Central Pneumatic compressor has a power supply issue.

If yours is the 2.5HP model running on a 120 Volt circuit, it will barely start with no issues given the power requirements of that motor.

The breaker would pop every time if the compressor was cold, as the thicker oil would add to the start load.

As far as the breaker goes, 20 AMP would be a lot better than 15 AMP for powering this compressor.

If you are using an extension cord, try plugging the compressor directly into the socket. Lose the extension cord. Any change? Please post a comment and let me know.

If not, then I suspect that it is not the breaker, but something in the start circuit. Start by checking the start capacitor. See that page on this site.

Cheers,

Bill

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Apr 29, 2015
Central Pneumatic 67847
by: Bill

"Which now we're gonna plug it into the power outlet for the dyer." Don't do it, Jennifer!

Dryer plugs should be special ones for 240 VAC and the motor on your compressor is 120 VAC, so, unless you rewire the motor to accept 240 you will fry it!

Plug the cord from the compressor into a standard wall socket that has few or preferably no other appliances pulling power from the same circuit and one that has a 20 amp breaker, if possible.

Add a comment here with your results if you would.

Apr 29, 2015
Central Pneumatic 21gal vertical cast iron air compressor
by: Jennifer

Hi Bill,
we purchased this air compressor model #67847 yesterday April 28,2015 from Harbor Freight and we're having some of the same problems. However, you did answer some of the problems we are having with this. First off, we had it powered to an extension cord. Which now we're gonna plug it into the power outlet for the dyer. Having said that do you think that will fix the problem we're having of it not building up to the correct PSI. Your definitely very knowledgeable with this type of air compressor. I'll give you our feedback after we plug it into an outlet instead of an extension cord. Honestly, I feel so stupid for doin that but we didn't know that it would affect how it would operate, but it makes total sense to plug it into a wall socket that is 240 instead of a cord. Thank you for all of your postigs, because its really helped us troubleshoot to get it working so we can enjoy building and fixing our projects around the house.
Sincerely,
Jennifer

May 12, 2014
Same issue
by: Doug

Sounds like the same thing mine is doing, but it is not tripping the breaker but the safety breaker on the machine itself.
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The safety breaker on the machine is likely a thermal switch, which suggests that your compressor motor is overheating, which is also a symptom of under-power to the motor, among other things.

B.

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95386 - could it be another problem if it will not hold air?

Where can I purchase a pressure switch for model number 95386? I have tryed to find it on line with no sucess. Also could it be another problem if it will not hold air.

Thank you
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Sam, you can use another vendor's pressure switch, as long as you can connect it up the same way as yours is. Take yours off, take it to the parts store, and find one that is similar.

What makes you think your pressure switch is the compressor problem? Is it leaking air?

If the issue is a pressure switch leak, where is the leak coming from? Is it actually the switch, or is it the unloader valve?

Comment here and let us know if you would so we can help you nail down your air compressor problem.

Cheers,

Bill

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Feb 06, 2013
Central pneumatic model 94667
by: Alex g

I got a 21 gallon compressor ,,,,,star and runs but don't built air pressure ....well just 10 psi I read some comment s like my....but I don't know ......thank

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67501 will not start?

by mitch
(Long Island)

Central Pneumatic air compressor 67501 (Photo: www.harborfreight.com)

Central Pneumatic air compressor 67501 (Photo: www.harborfreight.com)

I have a new CP67501 which ran fine out of the box. After a few minutes the pump will not start, only the cooling fan runs. Oil is at correct level. Out of Warranty - over 90 days. What can be the problem, please help.
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Mitch, as far as I know about this model, the fan is attached to the motor shaft. The motor shaft is also attached to the drive mechanism for the pump.

It seems to me then that if your compressor fan is running, then the motor is running. If the motor is running the pump should be pumping.

If the compressor pump isn't, it is possible that the motor shaft has uncoupled from the pump. Can you check that and let us know what you found as a comment here?

Cheers,

Bill

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Jun 22, 2016
Same problem
by: Anonymous

I have had the same problem only at 95 psi- would hold pressure and continue to run.
I put air tool oil in the spray nozzle.
took off Filter and cap.
Sprayed tool oil into the air intake mechinisms.

Ran Compressor while doing this- for curiosity.
Pressure built up to shut off compressor
It seems to fix the problem for now

Oct 29, 2012
fan only
by: mitch

Thanks Bill, but I checked the motor and fan, both are reciprocating; problem is that compressor pump does not engage. So it appeared that only the fan is running. How do I check if the shaft to the pump is engaged?
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No other way than to remove the shroud, dive into the innards where the shaft enters the bottom of the pump. The should be some sort of coupling there, and likely they are secured with a set screw or two, and it's them that I think may be your compressor problem.

B.

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