My 47065 won't build to rated pressure

by Harold
(Keystone Heights, FL.)

My 47065 is about 5 years old....Has worked great. However now it builds pressure to about 40 psi, shuts down. I wait a few seconds and hit the reset switch, it then builds another 5 to 10# of pressure and shuts down. I wait a few seconds and hit the reset switch only to have it shut down again after 5 to 10# of additional pressure..I replaced the pressure switch control valve but have the same issue.

What could still be the problem?
Hi Harold...

From what you have written, I don't believe this to be a pressure switch problem.

Rather, I think it is a power problem.

By that I mean that the motor is itself failing, but more likely, I think that the it is the power supply to the motor that is the problem.

Is the problem new? Are you, for example, using an extension cord now when you were not before?

If the power supply has not changed, then I suspect that your start/run or run capacitor may be the problem. If it is failing, your motor cannot get enough power supply to keep running against a building back-pressure load, your motor overheats, and goes off on reset.

There is a page on this site about how to test a cap.



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Jun 18, 2014
Overload Switch
by: Smokey

Hey Smokey here, I've been all the this before,
same problem over and over, all you need to do is replace the reset switch, the little switch on the
side of the motor close to the shut off switch,
this is a thermal overload switch just like a house breaker, it gets overloaded to many times and it goes bad. $3.?? and everything is back to
normal. Smokey
Thanks for that, Smokey. Good advice.


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Central Pneumatic #47065 stops at 40 PSI?

by Sam

Central Pneumatic air compressor 47065

Central Pneumatic air compressor 47065

I have a Central Pneumatic Vertical air compressor (Model # 47065-125PSI, 21 Gallon, 4.5 Peak HP). The compressor worked fine when it was purchased 3 years ago. Now, it will not build up to rated psi.

I put the valve control in the off position. I checked the oil to make sure it is adequate (on the specified red marker). I turn on the compressor to allow it to build up pressure. It takes about 15 minutes to reach 40 psi and stays there. The compressor never cuts off. I have let it run for a period of 30 minutes and no increase in pressure occurs.

After shutting off the compressor, the tank maintains a pressure of 40 psi (waited over 24 hours). I have not found any leaks ( I drained the tank using the valve underneath just for the hell of it - no changes).

Is it broken? Or , is there something quite simple I am missing. Clean the air filter? Adjustment?
Hi Sam. Yup, she's broken.

There are a bunch of reasons why your compressor won't build pressure, and topping that list are valves and gaskets.

See the sitemap page under troubleshooting. Read the info on the page about why air compressors won't build pressure, if you would.



Oct 23, 2011
by: AnonymouseEARL

I have same trouble with my model94667 it gos to 20 lbs and runs but wont pump up is this a piece of junk like to hear from some one from centeral pneumatic disapoited earl
Sep 25, 2011
by: Anonymous

Sam, I have the exact same unit except it only ran for one summer. Now motor runs but won't fill past 40psi and Harbor Freight doesn't want to even offer any support because they stopped selling them. Did you ever solve your problem? Hate to toss the thing since the motors running!
Aug 28, 2011
Your pressure valve is broken
by: Weirdnerd

Remove the four bolts on the piston head, remove the piston head carefully not to break the gasket, you will find there is an inverted "V" metal piece, remove it, (it has two Phillips head screws), under it there is a "flapper valve" made of thin spring steel, most likely that part is broken,and it will allow air to return to the piston, that part works as a "check valve" that prevents the air from the bottle to return into the piston. You can make a new "flapper valve" with a feeler gauge strip using an angle grinder and a #40 drill bit being very careful...That's what I did, make sure you hold the piece in a vise, and use gloves, safety glasses,or a full face grinding visor and thick clothing , steel shards can be very dangerous,and blood stains are hard to remove from clothing.

Once you have the "new" valve, reinstall it in reverse order as you disassembled it, make sure you tighten the bolts in a criss cross order, not to crush the gasket.
May 13, 2011
by: Anonymous

Good luck ordering parts, many of the gaskets are no longer available. Boggles the mind. If you are not comfortable making your own, then you're up the creek
Jan 21, 2011
Call Harbor Freight Parts
by: Anonymous

If you are getting a good amount of air blowing out the intake you probably need the following from Harbor Freight Parts:

28153 03B 47065 GASKET $1.00
28727 04B 47065 VALVE SEAT $2.37
28471 05B 47065 GASKET $1.00

A fairly inexpensive repair if your are comfortable with doing it yourself.
Jan 20, 2011
Broken Exhaust Valve
by: Anonymous

I have the same problem with A 40 PSI max. The exhaust valve is a horse shoe shaped reed valve that splits in the middle over time. I need a new valve plate and gasket set which I am in the process of ordering from HF.

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Jun 11, 2014
Same problem!!!
by: Anonymous

Have head off, found many leaks throughout lines, replaced check valve among other things. Went or clean inside head, found v shaped flapper valve, or intake//exhaust valve broke in half. Spring steel, you say I can make another with feeler gauge? Never saw a feeler gauge wider than 3/4". And has to be one piece
Thank you!
If a feeler gauge doesn't do it, try the blade from a good quality paint scraper, cut to size.


See a source here:

Please note: If you acquire a product using the Amazon link provided above, they will pay us a small commission which is used to help offset the cost of maintaining this website. Thanks!

May 10, 2013
losing pressure
by: AnonymousBill

I have the 21 gal Central pneumatic compressor from Harbor Freight. Had it for years.

Now only gets to about 40 lbs.

I heard air leaking around the shutoff switch. BIG label on it said 'NEVER REMOVE THIS COVER' no user serviceable parts inside. DO NOT REMOVE THIS LABEL.

Well that's where the leak is coming from. So I removed it. There you will find a spring tensioner that automatically shuts the unit off when it reaches max pressure, 125psi, but always shuts off before anyway, around 120psi.

There are 4 small bolts with nuts holding it down.

Under it you will find a rubber diaphragm about the size of a silver dollar. This is where the air flow is shutoff when max pressure is reached or when the power switch is pushed down.

This diaphragm can only be a 2 or 3 dollar part, but you can't get it anywhere.

What was once a perfectly good compressor, is now a useless piece of scrap metal. Thank you Central Pneumatic, and thank you Harbor Freight.
Sad but true. When the pressure switch diaphragm cracks and leaks, it is almost impossible to find parts.

However, a new pressure switch to replace the old can be had for around $35 or so, and that will breathe new life into your compressor, providing other parts aren't pooched as well.

Good luck.


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47065 Compressor kicks the Overload Switch?

by Larry

I have a Central Pneumatic model 47065 air compressor that keeps popping the Overload Switch when filling.

It was only filling about 8lbs of pressure and the switch would kick it off.

Did some trouble shooting, by passed the overload switch and problem solved.

The compressor fills to capacity and shuts off as its supposed to.

So where do I find the replacement Overload Switch? I have searched the net on the compressor, overload switches, and what looks to be the part number on the switch itself and so far no luck...
Larry, when you are referring to the overload switch, are you talking about the thermal overload reset button?

Sorry to be a little stupid here (not unusual for me) but if the thermal overload switch is tripping the compressor off, yes, it could be that the switch itself has failed, but could it not be happening too by it reacting to a thermal overload of the motor?

That could be caused by a poor electrical supply (not enough power to run the compressor motor), it could be caused by a run capacitor that is failing, and it could also be caused by a motor that is failing, among other reasons.

As to finding the switch, go to your Harbor Freight store (this is their house brand) and ask them where they send compressors to get fixed under warranty. That could be the source for a new switch.



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Oct 20, 2011
by: Larry

Bill since posting the original question I contacted Harbor Freight and the compressor model has been discontinued and the supplier no longer supplies parts. At my work we have a metrology and calibration lab so I took the thermal overload switch to them to see if they could find a replacement and while they had it they put it under load and tested it. The overload switch is working as it as supposed to. So, I will be looking at some of your recent suggestions. Thank you!


10-4 Larry. Keep us posted, if you would.


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47065 compressor will not turn on.

by Kirk
(Riverton, Utah)

I have checked to make sure the compressor is getting power; but it will just not turn on.

One day it worked fine, the next time I went to use it, it didn't.

Nothing, that I know of, happened to the unit to cause the problem. If anyone has any ideas to try, please e-mail me at Thanks!
Good that you know that the compressor is getting power, Kirk.

Did you dump all the air from the tank and try it again?

Is there power getting past the pressure switch to the motor circuit, in other words, has the pressure switch tripped to passing to allow power to flow through it to the motor circuit? If not, and with no air in the tank, it's likely the pressure switch.

See the troubleshooting section on why air compressors don't start for more tips, and add a comment here about the above if you wish.



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