Central Pneumatic Model 40400 – User Support & Info – Ask Here

Published Categorized as Air Compressor Troubleshooting, Central Pneumatic 23 Comments on Central Pneumatic Model 40400 – User Support & Info – Ask Here

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The Central Pneumatic Model 44400 air compressor is one model of the Central Pneumatic house brand sold by Harbor Freight air compressors.

The 40400 is a small, DIY type air compressor, and appears to be manufactured off-shore for Harbor Freight with a 2 HP motor positioned on the top of an 8 gallon tank, with pull handle and wheels under the tank for easier movement.

The 40400 is oil lubricated, and must be filled with compressor lubricating oil before being run for the first time. Check the oil level in the sump by looking at the sight glass located under the oil fill plug on one side of the pump. If filled to the correct level, oil will be visible in the sight glass, and level with the center of the dot in the middle of the sight glass. Do not overfill. If you do, use the drain plub below the sight glass to drain off excess oil.

Central Pneumatic 40400 Air Compressor
Central Pneumatic 40400 Air Compressor

With so many questions submitted about the operation of the model 40400, it has earned its own forum page here on about-air-compressors.com. If you are looking for help with your 40400 you will find it below.

Please do read the existing posts to see if your compressor issues has already been addressed. It’s also a good idea to review the troubleshooting pages too to see if your question has already been answered there as there, are many common compressor problems have already been addressed on those pages.

If you can offer advice on another visitor’s posting about their Central Pneumatic model 40400 air compressor, please do so by adding a comment on the existing question.

40400 Manual

Download a copy of the manual for the Central Pneumatic #40400 air compressor, by clicking here.

As the numbers of comments added to this page grows, it may get harder for you to find the specific answer you are seeking so I’ve added a search box here for your use to help you find the information you need.



Existing Central Pneumatic Compressor 40440 comments

Central Pneumatic 40400 has cheap parts

Central Pneumatic Compressor 40440 – good workhorse with cheap parts, check valve seems to be

Check valve blew on 40400 compressor

I have a Central Pneumatic 2HP 8 Gal compressor (40400) about 2 or 3 years old. I use it only about

Central Pneumatic will not stay running

I have a model 40400 compressor that will not turn on, what should i look for?

Unloader valve hose for 40400 compressor

Need to know what the part number is and where to buy the unloader tube for a Central Pneumatic 40400

Parts for a Central Pneumatic 40400

I can’t find connector to fit the compressor. I have tried a 3/8 inch and it is too big and a 1/4 inch is too small.

Source for CP 40400 pressure regulator

Where can I find a pressure regulator for the 40400? Is there a substitute that may work?

Pressure switch for CP 40400

I need the part which has been circled (oval) in the photo included. According to the manual’s diagram

Central Pneumatic 40400 won’t start


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Check valve went bad on 40400 so purchased replacement a couple of years ago. Finally putting it all back together and hooking up copper line off compressor. The 90 degree elbow off compressor head just crumbled as the compression nut started to tighten. Source for replacement?

There’s a good chance your local big box has something that’ll fit. It’s likely a standard part, but don’t know if it’s NPT or metric.
If you’re not familiar with NPT, look it up. It’s probably not what you think.

Good luck.

i’m looking a discharge copper tube for 40400 central pneumatic can you help me.

Does anyone know where I could source a new cooler fan for this compressor? I got mine off the side of the road and it’s been great but with it getting so hot I don’t want to break it.

I need a new air line that comes from the valve on the tank to the control box for the 40400 central pneumatic 2 hp 8 gallon air compressor!

I might ask why…
But if it’s fubar, take what’s left of it to a hardware store and try to mach it. Should be at least 100psi rated. It’s not normally subjected to sudden pressure, fwiw.

A followup re: the new pressure switch. The C/P 40400 is designed for max of 115 PSI. But the replacement switch (LF10-L4H) is pre-set for 95 (cut in) to 125 (cut out) PSI. By turning the switch adjusting bolt head exactly two revolutions counter-clockwise, cut in & cut out lowered to 85 / 115 PSI. So that’s about +/- 5 PSI per revolution. Hope this helps other users. Cheers!

We’re obliged. Thank you.

A solution to unit not pressurizing > 30 PSI. In another thread, it was suggested that the flexible diaphragm in the pressure switch had a crack or hole, thus letting air pass, and not shutting off. So I bought a new replacement switch. (Link removed. Please Google LF10-L4H Pressure switch to find sources. Thanks. Moderator)

After reassembling (teflon tape on all male threads), the unit pressurized and shut off normally. 🙂

Unit will not pressurize higher than ~30 PSI, and doesn’t shut off. Might it need a new air pressure switch? Or a new regulated valve (pressure selector)? I’ve already tightened both copper tubing end connections from compressor to tank. Thanks.

Did you forget to close the drain valve? No?
Then after it gets to 30, stop it it. Look/listen for leaks.
No leaks? Something is wrong with the pump, or perhaps the tube from the pump is cracked.

40400 won’t start, kicks the reset button. Removed motor cover, unhooked pressure line, reset button in, hand-turned fan while turning the switch on and runs fine?? Can rehook pressure and will build air, but it will not restart unless I go through the first procedure. I did lube rear motor bearing at the fan end, maybe help some, but not much. Any ideas ?? I bought this used for a friend and the guy said it worked fine, my bad for believing him I guess !! Anyway, if you can point me in the right direction I would very much… Read more »

“…hand-turned fan while turning the switch on and runs fine??”
With no tank pressure, will it start by itself?
When there is tank pressure, does it hold it, or drain off?
Does it make a noise before the breaker blows?

No, it won’t start by its self at all. Does hold pressure. No noise, just motor hum. I’ve ordered a capacitor that should be here in a couple of days. I really think that is the problem, but wasn’t for sure. Thanks

Yeah, if it’s the start cap. you’re getting.
There’s a set of contacts at the back end of the motor that may be burned/fused/grubby that may also be part of the problem.

Good luck.

Yes, it is the start capacitor a CBB60. Thanks for the heads on the motor contacts, I will take a look at that also. I do believe the root cause is the start capacitor as it takes very hand spin to make it run under no load (pressure pipe removed from the compressor head). Thanks again, Leroy

You’re right. Let us know when you get the part in…

Got the capacitor today, R&R and it started first try. Both were CBB60, but the replacement was a third smaller. FYI, I removed the compressor to install the new capacitor as I thought it would be quicker in the long run. You know, the hand of a midget and the grip of an ape thing, of which I have neither. Thanks again for your support !!! Leroy

And that you for confirming the fix.
It’s appreciated.
Have fun.

“Both were CBB60, but the replacement was a third smaller.”
Height, width, or some of each? It fit the mount OK?

Yep, smaller around and shorter, but rear mounting stud was in the center, so no problems at all. Thanks

Ah – stud mount. OK.