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Craftsman Air Compressor Not Building Pressure – Solutions & Reasons

Published Categorized as Air Compressor Not Building Pressure, Craftsman 1 Comment on Craftsman Air Compressor Not Building Pressure – Solutions & Reasons

This article will serve as a hub for all issues related to Craftsman air compressors not building pressure. It’s a very common problem for a Craftsman air compressor will not build pressure, and so, this article will present the reasons why this occurs, along with current reader questions and answers.

Table of Contents

Why My Craftsman Air Compressor Won’t Build Pressure

The most likely reasons why your Craftsman air compressor won’t build pressure are:

  • Compressor intake valve failing
  • Compressor pump pressure valve failing
  • Compressor gasket failure
  • Compressor piston seal failure
  • Tank check valve is compromised

Compressor intake valve failing

If the intake valve has failed, the compressor will draw air in through one cycle, but then that air will blow right back out the intake valve and out of the pump again when the piston is in the compression stroke.

Compressor pump pressure valve failing

If it is the pressure valve or pressure switch in the valve plate that is the source of the problem, air will flow into the tank through the pressure valve on the compression stroke, but then be drawn right back out of the tank as the piston cycle to try and draw more air in through the intake valve.

Compressor gasket failure

It is possible that your compressor is working fine, but as it is cycling, the air is flowing back and forth across a failed gasket inside the pump instead of being forced into the tank.

Compressor piston seal failure

The rings on the compressor pump act as seals, which prevent excess oil from being able to flow into the compressor’s cylinders. When this component is defective, the discharge head of the pump will receive a high pressure of air. It will affect the pump’s motor might and stop it from restarting anytime the tank is full.

Tank check valve is compromised

The tank check valve is designed to allow one-directional flow of the air from the compressor pump into the air tank. If the tank check valve has failed, air can leak back from the tank out through the compressor pump or various bleed and pressure relief valves on the pump circuit.

Please visit our Why an Air Compressor Won’t Build Pressure & How to Fix a Compressor Not Building Pressure guide for detailed information on each, along with how to conduct the necessary checks!

Reader Questions & Answers – Craftsman Compressor Won’t Build Pressure

3 Gallon Craftsman Air Compressor Won’t Build Pressure Over 25 PSI


I have read your posts and tore down my compressor. both reed valves are fine, gaskets look new, and piston rings look fine to me, checked the little white valve that is in the copper tube that goes to the switch… what else should I check?

The compressor runs but holds at 25 psi… note that due to not draining the air after use, I found a lot of dirty water in the tank when I removed the drain valve… could this have caused any damage to the unit? what else should I check and how would I check it?


Bob, good effort in trying to figure out what’s going on with your Craftsman compressor, and for the complete post. It helps me try to help you.

You say the air compressor holds at 25 PSI. I take that to mean that the compressor keeps running, and the pressure never goes past the 25 PSI, or does the compressor stop at 25PSI?

If the compressor shuts off at 25 PSI it’s the pressure switch that is causing the problem, I think.

However, if the pressure builds to 25 PSI and stays there with the compressor still running, and the motor doesn’t seem to overheat (indicating overload) then you have a pressure-related leak I suspect, and even though the valves and the gaskets look good on visual inspection, I think that under pressure one or both of these items are leaking.

Use a lighted match at the intake port to see if any air is huffing out while the compressor is running. If so, it’s a valve issue.

If not, then I’m going with a pressure-related gasket failure.


You are correct in that it keeps running… not sure if it would overheat as I never left it running more then10 seconds after pressure stopped building.

I will try the match trick and get back to you…where exactly do I hold the match near the intake… I don’t actually see any holes where it can be getting air into it? Will this test be affected by the air being blown by the big fan blade in the front… when I looked for leaks there was a lot of air moving around which seems to be from that fan


The issue is to determine whether the intake is pulling in the air or huffing it out while the compressor is running.

Big fan?

What size of compressor and model is yours, Bob? You have posted on the page about 3-gallon Craftsman air compressors.


Got it all back together (correctly I hope) and still no good….there is air coming out the fuel filter inlet…now that would mean bad valves right? but my valves look fine… is there something that could be wrong with them that I cant see?

I cant seem definitively say I see any leakage from the gaskets also…kinda hard to tell with that big fan even though I tried to block it off…

Question of the thin metal gasket between the two valve plates…one corner of the two openings has a slight rise in the shape of a triangle… how do I know where that should face? do I need to oil and of these valve parts or do anything special..used a little to hold the reeds in place


Not as much as I am now about what air compressor you are talking about.

Please add a few photos showing the overall compressor and one or two where you feel the problem is. Then we’ll proceed.

Craftsman 5 Gallon 1 HP Air Compressor Not Building Pressure


I have a Craftsman 5 gallon 1 horse direct-drive oil-lubricated cast cylinder air compressor.

I tried using two coil roofing nail guns on this compressor and now the thing doesn’t even build any pressure, I’ve checked the release valve it’s closed, and the exhaust seems to work right. What are your thoughts?


Why would you use two coil roofing nail guns on your poor compressor? What did it ever do to you? 🙂

Tried to find what model the 5-gallon Craftsman was, and didn’t find any of that tank size, so I guess yours has got some years on it?

Am I to understand that you have connected two air guns from the compressor discharge coupling, and neither gun is getting enough air to work?

There are many reasons why a compressor will run yet not build pressure in the tank. And if there’s no pressure in the tank, then the nail guns can’t run.

When the compressor shuts off (assuming it does) does air bleed out from the unloader valve constantly? That being the case, see the page about unloader valves on this site for help about that.

On the other hand, if your compressor is running continuously and not gathering any pressure in the tank, then it won’t ever reach cut out, and your unloader valve won’t ever open, so you have a different problem.

Rather than retype all the info already there, please visit the compressor troubleshooting pages about air compressors that run but don’t build pressure. The things you need to check are there. Please check them out and comment about what you found if you still need help.


If your air compressor builds pressure to a point, and then won’t go any higher, check your gaskets. If you take the compressor apart, be prepared to replace the gaskets as they are brittle after use and most likely will tear.

Check the gasket that divides the chambers by the air intake. Make sure that there is no part of the divider gasket missing. Even a small gap can cause pressure to cease building.

You can buy replacement gaskets for most brands, or you can buy a sheet of gasket material at an auto parts store for under $10 and cut your own. Try to keep the old gaskets intact as much as possible to use them as a template.

Model 919.152811 Craftsman Air Compressor Will Not Build Pressure


Compressor 919.152811 will not build more than 60 psi?


Mason, not a lot to go on here, buddy.

Are you saying the compressor gets to 60 PSI and stops, or are you saying the compressor gets to 60 PSI and keeps running, but the pressure doesn’t go higher?

If the first, then the pressure switch is suspect.

If the second, then pop over to the troubleshooting section on the sitemap page and follow the link to the pages about why air compressors run but don’t build pressure. Once you get that read, do the checks on your compressor, then post a comment here with what you found.


Found out why it keeps running but won’t go over 60 psi… reed valves are broken! New ones ordered…

Thank you for your reply.


Glad you were able to nail it down. I always suggest a new gasket kit if you are replacing the valve plate.

Craftsman 921.166460 Air Compressor Will Not Build Pressure


The compressor appears to compress the air but there is no air at the hose. This is a Craftsman model 921.166460 with a 5-gallon tank on a nice little cart. I have replaced the gaskets, sprayed the unit with soapy water, and verified that there are no leaks. I checked before and after the check valve and have compressed air. Both gauges do not show any pressure and there is none when I connect the hose. — Where is all that is the compressed air going to? Again, the soap test shows no leaks anywhere.

Meanwhile, I recently purchased a similar small Campbell Hausfeld at a yard sale with an 8-gallon tank. There was no air at the hose port (no quick connection or hose either, but I replaced those). I assumed it was the gaskets and replaced them but still had no air at the hose — but there was air blowing out of the check valve and a “black worm” hanging out of the valve, as well. I replaced the “o” ring (the black worm) in the check valve and the unit is now running like a top.

What have I overlooked in the Craftsman?


Jeff, a photo of the Craftsman 921.166460 compressor would help all of us figure out what’s going on. I couldn’t find a photo of this one anywhere.

Anyway, let’s work on this. You say “Both gauges do not show any pressure”. That strongly suggests there’s no air in the tank. That is unless the feed tube that leads to the tank gauge, the regulator and regulator gauge, and the coupler into which you push the air hose to connect is blocked, and that I’ve never heard of happening.

Or, the gauges are broken and there is air in the tank. Let’s check.

If the gauges work, and there is no blockage after the compressor has been running for a few minutes, crack open the tank drain. What happens? Does any air bleed out? If so, let it all bleed out for now as there may have been residual air in there from before the failure. Close the drain, run the compressor for 3-4 minutes, and open the drain again. Any air bleeding out?

If not, then that compressor cannot be building pressure, else it would show on the tank gauge.

Does this model have lubrication? Is there an oil fill port under the dipstick? While the compressor is running, is air blowing out the dipstick cover? Enough for you to feel? If so, this compressor may have a significant piston seal leak, and all the air that’s being built is blowing out the oil fill vent hole and not going into the tank.


Thanks, Bill — but what’s the fix?

I have disassembled and re-assemble portions of tracking the air… It is blowing compressed out of the head cylinder and beyond the check valve and beyond the safety valve but, apparently, it is losing it somewhere between there and the gauges and tank.

The compressor is lubricated by oil but it has no dipstick. Rather, it has a sort of 2-inch black “top hat” cap on top and a visible glass port on the side where you are to keep the oil just above its red dot. It is not blowing air out the “top hat”.

I will admit that I did, at one point, over-filed it with oil but now we are just above the red dot. If you overfill it (and I did), it will blow oil out of the “top hat”.

Whaddya think the problem/fix is?


Just FYI Jeff, filling the oil level to the middle of the center of the dot in the sight glass shows the correct “full” reading for that compressor.

If both gauges are not showing pressure and assuming they work, then the compressor is NOT building pressure, simply moving a small amount of air that may feel like pressure buildup, but isn’t really.

When you say “It is blowing compressed out of the head cylinder” can you explain further how you know that? If it is true, it suggests that there is a gasket failure, and the pressure that’s being built by the cycling of the piston is cycling from a slightly higher pressure level to lower through a gasket. That’s going to require a gasket replacement if that’s happening, and that means opening up the pump.

If no air is blowing oil out of the “top hat” that suggests that the piston seal is OK. This is probably a splash-lubed compressor and I guess oil could splash up the fill tube and out yet there should be virtually no air in the sump to blow it out.

Once again, the absence of any photo of the compressor, compressor pump, and areas you are referring to is making this quite difficult to resolve.

Once again, if the pump is cycling with the motor running, and both gauges are not registering pressure build-up in the tank and both gauges are fine, then the pump is not compressing air.

The logical reasons are damaged seals in the cylinder, the valves are broken or jammed, or any pump head gaskets have been breached, which pretty much sums up what should have to be at fault for no air build.

Open the pump and find the fault in those and fix it and if the motor runs properly the compressor will then generate pressure. Good luck.


Jeff, can you double-check that model number? I’m not finding it.
And if you open the tank drain valve, do you get air for a few seconds? Doug from s.d.ca.


Thanks, Doug

You are right the correct model number is 921.166360. (not 921.166460).

As you suggested, I opened the tank’s drain valve; there is no air in the tank.

As I said, it appears there is compressed air coming out of the cylinder head, out of the check valve, through the pressure tube assembly — but:

there is no air at the safety valve and beyond OR in the tank. All the gauges are not moving at all. I can not figure out where all the air is going.

I am open to all suggestions.— thanks again.


Doug says,

I presume you’ve found the parts diagram and list for this. I’d suspect either of these, from what you’ve said:


00049 PRESSURE RELIEF TUBE ASSY. 16636 $3.18

Additionally, if both of those are unbroken and connected properly, that would leave the unloader valve in the pressure switch connected by 00049. It’s $44, but you can probably get something off the shelf for much less if that’s the trouble.

Good luck.

FAQs (Frequently Asked Questions)

Why does my Craftsman air compressor not build pressure?

The most common reasons why your Craftsman air compressor won’t build pressure are the intake valve failing, pump pressure valve failing, gasket failure, piston seal failure, or the tank check valve being compromised.

If you have any questions about Craftsman air compressor not building pressure, please leave a comment below, with a photo if applicable, so that someone can help you!

By Aidan Weeks

A passionate Mechanical Engineer with endless enthusiasm for fluid power - building off the back of over 18 years of high quality contribution and discussion stimulated by Bill Wade here at About Air Compressors. With both practical and theoretical experience in pneumatics and hydraulics, I'm putting my knowledge to work - and working my grey-matter through my research, assistance and publishing work here at About Air Compressors. Feel free to reach out any time! P.S. A HUGE shout out to Doug who really offers such great value to all visitors to About Air Compressors - once again, feeling like I'm standing on the shoulders of GIANTS by getting to work alongside such a great community

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