Air Compressor Troubleshooting, Solutions, Common Problems & Causes

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Is your air compressor not working? Whether the problem is electrical, the motor, the regulators, or the valves, determine why your air compressor is not working with this simple air compressor troubleshooting chart.

Table of Contents

Air Compressor Troubleshooting Guide – How to Fix an Air Compressor

It’s actually not difficult to repair air compressors. They have few moving parts and are very reliable. Parts are readily available for most compressors, and with some basic air compressor motor troubleshooting, you should be able to nail down what’s wrong on your own.

Is your air compressor not functioning as expected? Don’t worry, here are the air compressor problems and solutions to get it back up and running in no time.

From air compressor troubleshooting, and finding spare parts to testing a compressor – we’ve got you covered!

Troubleshooting Your Compressor – Air Compressor Troubleshooting Chart

Air Compressor Problems and Solutions

Compressor Won’t Start Troubleshooting

ProblemCausePossible Solution
Compressor won’t startBasic starting troubleshooting—start hereCompressor will not start
Cold weatherCompressor will not start cold
Compressor won't restart after filling the tankCompressor will not re-start
If there is air in the tank, the unloader valve may be badCompressor struggling to restart
Compressor won’t start with air in tank
Problem with the capacitorCompressor cuts off on refill
Compressor will not start unless tank empty
Centrifugal starter failingCompressor with HP motor will not start
Bad CompressorBrand new compressor won’t run

Compressor Running Issues Troubleshooting

ProblemCausePossible Solution
Compressor running issuesBasic bogging down troubleshooting guide —start hereAir compressor bogs down
Compressor starts then stopsCompressor starts and stops
Thermal cutoff/rest button trippingCompressor reset keeps tripping
Compressor shuts down before reaching pressure
Compressor blows motor breaker
Motor failingMotor turns slow and trips the breaker
Wrong sized motorBogs down while running
Compressor hums but does not build up pressureCompressor hums and stops
Blows breaker after a few revolutions
Faulty reset buttonCompressor runs only when reset button is held
Compressor runs but never reaches stopping pressure

Compressor Won’t Stop Running

ProblemCausePossible Solution
Compressor won’t stop runningStopping issues overview — start hereCompressor slows and stops
Compressor will not cut off
Air leaks or bad sealsCompressor will not shut off
Bad Pressure Relief Valve (PRV)Compressor won’t shut off like it should
Converting motor from 220V to 120VChange compressor wall plug from 220 V

Electrical Issues Troubleshooting

ProblemCausePossible Solution
Electrical issuesElectrical wiring troubleshooting — start hereElectric troubleshooting air compressors
Converting motor from 220V to 120VChange compressor wall plug from 220 V

Fuse or Breakers Popping Troubleshooting

ProblemCausePossible Solution
Fuses or breakers poppingHome circuit breaker trippingCommon fix for tripping breaker
Compressor blows breaker or fuse
Air compressor blowing circuit
Compressor blows breaker or fuse while running
Motor overheating—thermal resetCompressor motor keeps popping the reset
Compressor blows motor breaker
Motor failingMotor turns slow and trips the breaker
Breaker pops when motor restartsCompressor runs five seconds then trips breaker
Bad wiringHeard a spark and compressor won’t start
ProblemCausePossible Solution
Low air flow and related issuesIncorrect compressor for tools selectedUnderstanding CFM Measurements
Increase air output by using two compressors togetherCombining two air compressors together
Insufficient air pressureWays to increase SCFM of a compressor
No air coming out at all? Start with this troubleshooting guideNo air out of hose
Air lines freezing in cold weatherCompressor air lines freeze up
Pressure dropping in tool supply linePressure drop in air lines
Average air tool SCFM

Capacitor Issues Troubleshooting

ProblemCausePossible Solution
Capacitor issuesPossible bad capacitor, test with multimeterTesting compressor capacitors
Poor electrical connections or excessive vibrationCapacitor keeps blowing
Mechanical wear or failure of compressorPiston head heats up and capacitor blows
Incorrect wiringStart capacitor keeps blowing
Incorrect capacitor on motorWhat Capacitor Does My Compressor Need

Liquid Fuel Air Compressors Troubleshooting

ProblemCausePossible Solution
Liquid fueled air compressors (Gas – Diesel-Propane)Engine stallsEngine shuts down when tank full instead of idling
Carburetor ProblemsEngine dies when throttling back up

Lubricators Troubleshooting

ProblemCausePossible Solution
LubricatorsAdjusting drips per minute on an air line lubricatorDrips per minute for an air line lubricator
Installing an air line lubricatorSetting up and operating an air line lubricator

Air Compressor Motor Troubleshooting

ProblemCausePossible Solution
Air compressor motor troubleshootingMotor overviewCompressor motor problems
Motor makes a humming noiseHumming air compressor
Motor hums and compressor won’t start
Calculating correct capacitor sizeWhat capacitor does my compressor motor need
Motor surgesCompressor motor surging
Motor sparks and smokesCompressor motor sparking and smoking
Reset button Trips ContinuouslyCompressor runs only when reset button is held
Bad Thermal ResetHow to buy a replacement thermal cut out
Incorrect motor voltageChanging compressor motor voltages
ProblemCausePossible Solution
Oil related issuesOil issue troubleshooting — start hereOil related issues
Compressor has an oil issue
Changing the compressor oilHow to change the compressor oil
Air in oil or too much oilAir comes out of the oil fill cap
Why does oil come out of the oil fill tube
Too much oil damaged my air compressor
Burnt oil smell coming from compressor
ProblemCausePossible Solution
Parts related issuesReed ValvesMake your own compressor reed valves
Reed valve material
ManifoldMake your own compressor manifold
GasketsMake your own compressor gaskets
How to Test CapacitorsTesting capacitors
Cooling FansBroken compressor cooling fan
GaugesAbout air gauges

Pressure-Related Compressor Issues Troubleshooting

ProblemCausePossible Solution
Pressure related compressor issuesNo pressure build upCompressor will not build pressure
Compressor — why  not build pressure
Regulator leaks airWhy a compressor regulator leaks
Air comes out of intakeAir comes out of the compressor intake filter or port
Reed valve failureReed valve failure
Pressure switch problemsRuns and pumps but builds little or no pressure
Compressor pressure problem
Compressor won't hold pressureCompressor loses pressure quickly
My compressor will not build pressure
Can’t get compressor to fill over 47 PSI
How long should a compressor hold air
Compressor won’t pump at 80-90 PSI

Pressure Switch-Related Troubleshooting

ProblemCausePossible Solution
Pressure switch relatedReplacing your pressure switchHow to buy a new compressor pressure switch
Buying a compressor pressure switch
Has pressure switch issues
Broken compressor pressure switch
Find pressure switch E247030 
Repairing a pressure switchPut my pressure switch back together
Putting a pressure switch back together
Fenwai pressure switch rebuild
Replace spring in pressure switch
Pressure switch air leakAir leaking at the unloader valve on the pressure switch
Condor pressure switch leaking
Condor pressure switch manual
Lefoo LF10-4H pressure switch unloader
Pressure switch disconnect problemsLine comes off the pressure switch
Pressure switch contacts keep burning out
Compressor cut off not working
Broken compressor switch manifold
Plastic hose blows out of pressure switch

PRV (pressure relief valves) Troubleshooting

ProblemCausePossible Solution
PRV (pressure relief valves)All about pressure relief valves — start hereAbout the PRV
When PRV valve opens
PRV repairFix a PRV
PRV keeps cracking open

Unloader Valve Issues Troubleshooting

ProblemCausePossible Solution
Unloader valve issuesUnloader valve issues
Air compressor not unloading
Air leaking at the unloader valve on the pressure switch
Adjusting the compressor unloader valve
Do I need an unloader valve on my switch
Unloader not functioning or not present

Pumps Troubleshooting

ProblemCausePossible Solution
PumpsAll about pumps — start hereAir compressor pumps page
Repair proceduresB5900 pump repair steps
Should intake valve be blowing air out
Pump pulley rotationPump pulley rotation – is it important

Regulators Troubleshooting

ProblemCausePossible Solution
RegulatorsAll about regulators — start hereAbout regulators
Fixing an air regulator
Regulator questions
Regulator hissing or leaking airRegulator hissing – leaking air
Regulator knob replacement on Sanborn

Tank Issues Troubleshooting

ProblemCausePossible Solution
Tank issuesHow to drain a compressor tankHow to drain the compressor tank
Calculating tank sizeGallons to cubic feet (air tank size)
Cleaning tankCleaning inside of a compressor tank
How to add an air tankAdd an air tank
Can I put two tanks on one compressor
Add an additional air tank to the system
Tank recycling
Use propane tank for air compressor
Water in the compressor tankCompressor water in the tank
Condensate is a problem
Increasing tank pressure
Tank pressure margins
Tank check valve issuesTank check valve
How to buy a replacement compressor tank check valve
Compressor tank exploded

Air Tool Issues Troubleshooting

ProblemCausePossible Solution
Air tool issuesAir flow issues with toolsAverage air tool SCFM
Compressor can’t keep up with air tool
Compressor won’t run air tool
How long will this air tool run
Nail gunsWon’t shoot nails
When using my nail gun the compressor won’t shut off
Compressor to run 4 roofing nail guns
Air supply for flooring nail gun
Blow gunsBlow gun not working
Spray gunsSpray gun and compressor size
Pressure drop in HVLP paint sprayer
Can this compressor run my HVLP spry gun
Die grindersIs a higher CFM die grinder better than a low CFM one
Pressure required for die grinder
Air sandersWhat air sanders can I use
Impact wrenchesImpact wrench air consumption
Need impact wrench for lug nuts
Impact wrench has loss of pressure during use

Miscellaneous Compressor Troubleshooting

ProblemCausePossible Solution
Miscellaneous compressor troubleshootingCFM calculationsCFM – cubic feet per minute
CFM-SCFM issuesCFM – SCFM compressor flow issues
Compressor maintenanceBasic compressor maintenance guide
Flywheel direction of rotationDirection of compressor flywheel
Hot compressor linesWhy does my compressor line get hot
Basic Troubleshooting Guide 2Troubleshooting compressors three (smoking, too hot)
Laying compressor flatLay a vertical 5.5 HP compressor flat
Oil out of breather holePump blowing oil out the breather hole
Water in the linesDewpoint and water in the lines
Dealing with compressor generated water
Compressor air lines freeze up
Basic Troubleshooting Guide 1Troubleshooting compressors one
Underground pipe problemsUnderground air line
Repair issues to watch out forSome compressor repair issues
Spark then starting problemHeard a spark and now compressor won’t start
Setting up dual compressorsDual air compressor set up
PVC pipe problemsPVC pipe swelling and bursting

How to Fix an Air Compressor – Any Brand, Any Problem!

Do you have a specific air compressor problem?

Before you post a question here, visit this page with a list of all the top air compressor brands. If the page doesn’t have an answer for you, use the form on that brand page to ask a question about it. That makes it easier for folks with the same one to solve problems for their compressors. And you might find the answer to your question has already been asked and answered!

If your air compressor brand is not listed, please use the search box top left to find an answer to your specific air compressor troubleshooting question on this site.

If you still can’t find any information on your problem, please post your question at the end of this page. We, that’s me, and the many visitors to will try to help you out with your air compressor problem.

If you can help another compressor user by commenting on their compressor problem, that would surely help all of us, and we all thank you for that.

Please leave your comments below, and let’s try to get your air compressor problem solved.

FAQs (Frequently Asked Questions)

What are 3 common issues problems with a pneumatic air compressor?

Some of the most common issues with an air compressor are air leaks, insufficient lubrication, and the compressor overheating causing the circuit breaker to trip and halt operations.

What is the most common cause of air compressor failure?

No doubt the biggest cause of air compressor failure is overheating, which leads to the compressor burning out and failing. If air compressors are overworked, by exceeding their duty cycle it is very likely that excessive strain will be thrown onto the compressor, causing premature wear and tear.

What causes a compressor not to build up pressure?

A defective reed valve is a common reason why your compressor may not be able to build pressure. A defective reed valve will allow air to exhaust out from the air inlet. It could also be a leak somewhere else in the system blocking the compressor from getting past a certain point.

What to do if air compressor is not working?

If you air compressor is not working, you should first aim to diagnose what the issue is. Is there a problem with the power supply? Do you have blown circuit breakers? Do you have insufficient oil? Visit our air compressor troubleshooting guide for further checks.

Additional Troubleshooting Pages

Air Compressor Types Troubleshooting

Air Compressor Brand Specific Troubleshooting

Air Compressor Brand/Problem Specific Troubleshooting

Air Compressor Part Specific Troubleshooting

If you have any questions regarding air compressor troubleshooting, 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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Atlas copco rotary air compressor trips frequently on starter feedback contact open. Please suggest resolution..Thanks

I have a grimmerschmidt 250 DR rotary screw pull behind compressor. When i shut compressor off it blows all its oil out the air lines and the silencer on the pilot valve. I can’t find any information as to what might cause this. Would appreciate some help in figuring out what is causing issue.

The problem: there’s a warning sign appearing on the compressor icon on the main display without mentioning the cause of the problem, at the same time, on the compressor main controller display which is Electronicon III -MKIV(D controller) shows ” lan control A” instead the normal statement” lan control D”
Then I have to reset from the ES controller.
I hope I could solve this after installing the program, or if you have any suggestions, I would be grateful.

Thank you

It stood out to me when you mentioned that it is not difficult to repair air compressors. My brother wants to purchase an air compressor. It could be a good idea for my brother to find a professional that can fix the air compressor should it ever have any issues.

I have an old P185B IR compressor and it keeps tripping the air regulator button. The button you push the get it to air up. you push it in the compressor speeds up produces air to 120 psi then it trips and back down to idle.

As far as you describe, that’s how they work. Except usually 100 psi.
What happens after that? Is it blowing down?


Have you been doing the pre-start as described in the attached?
Also, can you send a pic of your control panel I can see what’s available there?
And after it goes back to idle, is there any pressure at all?

Screenshot from 2022-05-09 00-15-20.png

I stupidly left an older models drain plug open, left for 40 minutes the whole time compressor was running. Got back , finally realizing what I did when it shut off but never started again. Seems to be getting power, and flywheel turns when I manually turn it. Don’t see a reset button, and never had an issue before. Sorry, don’t have the make and model, but wired directly to a 20 amp breaker. Directly to a breaker anyway. Thanks!

It shut down by itself?
Then I’d turn off the breaker and check for continuity across the motor, as close as possible to the input. If that’s good, then check from those to the AC input lines. Probably one side will be open – try to trace the open back – you’ll probably run into a fuse or breaker.
Of course, if the motor winding is open…nevermind.
Good luck.

Hi. I have a Kellogg 335tv that just started giving me problems. The electric motor labors really hard at about 40psi (sometimes 45psi). The motor labors so hard that it will stop and humm. If I don’t shut off breaker it will trip.
I have checked numerous things…disk valves, tank check valve, no line blockages, etc. Anybody had this problem on their kellogg 335? Thanks

So I am concerned about the bit of rust in my SpeedAire tank…(I don’t know what the value of “bit” is.) I think it’s 60 gallons? Add oil to the tank? NO! You will never be able to use it for…if oil is in the air. Okay. A rust removal, like naval jelly or Evapo-Rust? Good luck coating the entire inside and the cost! Okay. I have just assembled a 18 gallon electrolysis rust removal setup. I have to use this now that I have time invested into it. —Using the wire wheel is getting timely expensive. But it removes… Read more »

SpeedAire #3z424e twin piston single stage, 2 HP. I ‘m trying to find information for a proper oil level. I don’t know if the plug is stock. If it was, I’m thinking it should be filled to the bottom of the fill port. I drained the old oil out a few days ago. It was bad. Filled it with Synthetic oil but it seemmed to not like being filled that full. Drained out about a cup and it did start easier. But now it seemed noisier than I remember. I added some regular 10 – 30 to bring it back… Read more »

If the pump looks like this one:
Then yeah, bottom of the threads of the vertical plug on the right.
You should try for single viscosity synthetic, although some have used Mobil1 with success.

That’s the one. Other than the plug is more to the right. The compressor has been running okay. It does pick up speed for about the first 10 seconds. Probably due to the little bit of heavy oil in it. Getting some now, as I am writing this, my brother is at the Auto Zone. (Getting a brake light switch retainer clip for a GM pickup. The switch malfunctioned as it was loose.No clip. Also the truck sat for 10 years. Amazingly!!! the plastic switch was made without high frequency plastic welding. Just 5 clips. A good pencil eraser and…better… Read more »

So, on a separate note.
My SpeedAire #3z424e twin piston single stage has only a plug where the oil is added. Any idea what the proper level should be?

Please disregard last post… I have a Quincy -15 Model # qt15 st 1500652 air compressor in my workshop.. Which is now my back up compressor.However when I energize my Quincy 15. Compressor It Continuess to run after 125#. (Approximately 45-50 seconds) after this point I hear this unusual inner hissing Noise. After about 8-10 seconds of this I switch off power. What cloud be my issue or issues

The safety pressure release valve? This is my first thought for the hissing.
The compressor running past its cut-off is probably the switch malfunctioning or some one has readjusted it to a higher pressure cut-off. Has anybody else, other than you, been using your air compressor?

I have aa Quincy QT -15. Model #qt15 st 1500652 compressor in iny work shop. Runs up up to o,,,125# and continues to run the sound changes to low vulume pressure as that continues pressure gauge slowly continue to rise and both heads.. The only way to stop it is to shut off the service disconnect. What could be the issue???

I have a Craftsman model 919167783 H.P. 1.6 25 Gal. displacement 6.4cfm Max PSI 175 Air delivery [email protected] RPM 1725 it takes for ever to build up pressure what will cause that

Bad rings, valves, gaskets. Loose pipe connections, drain valve open. Among other things.
Does it ever get to 175 or does it top out lower and keep running?

In addition to what Doug said, Has this been happening gradually or suddenly?
Also, Did it maybe sit unused for a long period of time?
This may help your diagnose—diagnosing—diagnostic…one of those.

Hello, I have a Magna Force single cycle twin cylinder air compressor. For some reason one cylinder quit sucking in air. I have good knowledge of engines but never worked on a compressor, so I have no idea what it would be. Thanks for any advice, Corey Proctor in Southern Illinois.

Valves. You know carbs? Same idea, but no gas. Cylinder down draws air, that valve closes when cylinder goes back up, forcing air back out through exhaust valve. If the exhaust valve is broken, it stops drawing. The valves usually are just some kind of flapper thing. You may be able to buy replacements, or make them from e.g. feeler gauge material, depending on the pump.

HTH, and good luck.
P.S. – You may have the same with gaskets – might have to make them. Pumps get hot, so engine gasket sheet.

Sort of like a two stroke but all ports are on top.

Yeah, right.

how to adjust belt tenson on speedaire 5hp compressor

Finger pressure in the middle of the belt should move about a half inch. Be sure the pulleys are aligned before you tighten down the motor.

I guess I’ll DIY…again.

Details that have brought me to this point below. When turning the pump by hand, is that under pressure or no pressure? And what am I really looking for? Just how easy is it to open the check valve under pressure? Have a SpeedAire #3z424e twin piston single stage, 2 HP, wired for 110v. It has been stored in a barn for about 3 years. 6 weeks ago, we moved the SpeedAire up to the house to check it out. Checked the oil, put a newer heavy plug on its 14 gauge extended cord and re-did all the connections and… Read more »


Hey Mark,

Sounds like you’ve done a fair deal of troubleshooting already. Rather than try and give some generic advice, I thought I’d point you in the direction of some specific issues some people have had that have been similar – and the solutions they put in place (you may not have read through them).

Have you tested the motor capacitor?

The short story above is short in comparison to my original write. I thought I should shorten it to just the key points. As for the capacitor: “Checked the starting capacitor and it charges both ways. But I couldn’t find a meter that could check capacitance. Well, that is partially true. I did borrow one but it only went up to 20 mfd. My start capacitor is 500 mfd. I have considered the breaker or house wiring. Call me arrogant, but I just installed the sub panel and wiring 2 years ago so it can’t be that….??? Okay. this I… Read more »

Checking the wiring is not infrequently the problem. But since you did it, that won’t be it. 🙄
However, does it have a *RUN* cap to check? That’s what it sounds like if it’s not the wiring.

“put a newer heavy plug on its 14 gauge extended cord ” How long is it?
You checked the run cap, right?
So that probably means you have a bad exhaust valve in one of the cylinders. At 70psi the pump is probably seeing 140 or more on the other cylinder.
If that pump is what it looks like, you can probably make the valves and gaskets with stuff you have laying around…

Good luck, and keep us posted, please.

I have found a possible kit. I’m just not sure if it’s correct. I will invest more into it. Considering that it will work. Have been trying to get a quote from AAA Electric Motors for a motor test. Another consideration. Strangest thing that their phone number or email is not working. The cord has been on the machine for some years. It was that old style plug. You know the type that used cardboard to cover the connections. And I still am not sure about that breather hole and the air intake. How to put on a better… Read more »

Well, if it’s starting at all, then the cap probably isn’t the problem. But valves certainly could be.
The filter is just a piece of felt. You could try foam, just be sure there’s something like wire cloth behind it to keep it out of the pump…

Oh yeah! No running capacitor. And are you referring to the reed valves?

Thing about the breather hole. I did not mention in my first post…because… I first thought it was a oil point for that part of the crank. ??? I know or I do know now. But, after I reassembled the motor and mounted it I noticed the little screw I placed in it, to keep dust from getting in, had bounced/ fell out. It was just setting in there. I had a better idea. Since I didn’t have a rubber plug I used a little rubber tube and screwed in a small screw. That wasn’t going to fall out. Yup.… Read more »

“It ran until it reached 70lbs. Then blew the breaker.” A breaker on the motor or your panel? 20A?
And I think it’s time to check the pump – Remove the output line, see if it “sucks” twice per rev at the intake, and “blows” twice at the output.
Unless you’re in a really dusty place, I wouldn’t mess with a fancy filer – paper or felt should be fine.

I haven’t given up yet. Just a break from one projects frustration to a few others. Generators and riding lawn mowers. Your instructions for checking the pump. Checking the output line should be straight forward. At the intakes…I think it should suck once at each intake per revolution…Normally? —————————————————————————————————– And when it comes to dust…I refer to this area as, “The Dust Bowl.” And when the wind really picks up, (about 3:30 4 or 5 days of the week) you don’t want to have any thing susceptible to fine dirt opened up. If it isn’t the dust, it’s the rats… Read more »

I can relate, and lol’d reading your dust bowl section. And I can relate.

The oiled filter idea might be something you could use – as in a small sheet metal intake with some oiled, fine, steel wool in it.

I really need to get back to this compressor.
It’s like I need to fix something but the tool I need, needs to be fixed. And fixing that requires finishing an earlier project and…

Will keep you posted.

Okay! I am finally back with more heart pumping, gut wrenching and some thoughts I will leave unexpressed. Except for this. ——- The short version: Apparently, when I reassembled the motor, back in May, I did not connect the wires correctly on the terminal plate. This should had been checked after I started having problems. ——- The long version for those interested or curious of how many other mistakes I make: Still working towards, moving to Missouri. I have come across more air hoses and fittings long forgotten about. I now have enough air hose to go from the garage… Read more »

So I just realized that some references in this last post did not make it into the final print in my first post. In my attempts to shorten my original post things were cut out. How do I edit this or can I?

There’s probably an option for editing, but it’s unavailable to us users. You can copy what you already posted, then edit and repost, though. Still sounds like the speedaire has a bad cap. Did you try your big cap with it at 220? Assuming the cap can take it, of course.
Maybe (re)check the unloader too, if you haven’t already.

compressor is set at 100 psi but sometimes won’t start up until the psi drops { or I physically release air ] to about 40 psi. Is this just an adjustment issue ?

Probably. What compressor are we talking about?

I would for starters, check your plug outlet especially if your in a older home. I have seen this happen where a seasonal AC was plugged in. One year it actually blew the breaker. The house wires were no longer tightly connected or screwed on tightly. This is my scenario as to how this would happen: A plug outlet that has a high current drawing device can actually heat up. Maybe just a little, but this constant temperature up then down, expand, then contract can slowly loosen the receptacle screw connection to the wire, very,very little at a time. Over… Read more »

Check the unloader valve operation.

Hi, when I start the compressor sparks come off the conduction plate beside the fan. The plate then retracts and then blows the fuse. I stripped the starter box and cleaned the pistons and head all of which are working fine.
happens about 5 seconds after starting the compressor. Has anyone had this issue before or fixes for this? It is a 200l TMUS compressor.

Can you supply either some pix of where the sparks come from, or at least a link to one?

Get a volt meter and start looking for AC current between ground and the conduction plate. I’m not sure what that is. But still, Does it have a running capacitor? 5 seconds in and maybe it’s failing bad.

Every couple of weeks my IR fails to keep up and no changes or added tools to the system. It wont go past 60psi. We stop working for a while and let it catch up till it shuts off at 120 psi., then continue to work as normal and it works fine. Then just randomly after a couple of weeks the problem returns. WTH?

Be nice to know what model…
But sounds like maybe there’s a bit of crud fouling the valve(s) from time to time.
I’m thinking it’s not making strange noises or anything and it continues to tun until it starts working normally.

It comes with protective rubber leg covers that help absorb vibrations and protect the floor against damage. Buy-on-Amazon

Hi I have a Hydrovane 15 my problem is that I have a huge amount of oil in my air and in the tank…I have changed oil seperator ….any ideas where to look?…the red oil is coming out pink and mushy!…Ione thing I do know is it has its own pressure cut of built in end of compressor that does not work it now relies on a seperate cut of switch that cuts off at 100 psi any help appreciated thanks

Maybe a stuck vane or some other internal leak. Mush indicates the oil has air bubbles.

Hello my delta force air compressor 3hp is blowing the air out the breather at the top of the cylinder and I’m getting no build up can you help me out .

Post moved to this page.

Sure. Most likely you have broken intake valve(s).
Scroll up (or down from the top) to :
Pressure related compressor Issues
for more info.

Good luck.

Bill, thanks for the opportunity to ask questions. my comp. is set to 90lbs. As I drive nails the pressure drops to about 65 lbs.and nails won’t drive in and comp. doesn’t kick on until I release more air thru an air/water separator then it will start up and build pressure up to 90lbs. again. Can you help ? thanks, Joe B

Knowing the model of your machine would likely help…

But, it sounds like your pump is stopping at 90psi? That’s probably too low. The 25psi difference between cut-out and re-start is normal.
If your cut-out were 115psi, you could set your regulator to 90psi and then the pump would restart, and you’d always have 90psi for your nail gun.

I’m guessing you don’t know how to do that, but you can find out on the pressure switch pages. If that doesn’t work for you, give your model number and we can help.

There should be an adjustment on the pressure switch to adjust the high and the low. Thats how mine is anyway.

Still learning how to navigate this website properly. Please let me know if this has a more appropriate location. I have a 3Z170B that came with a shop that I purchased. To date it’s done nothing for me. I can’t even figure out how to turn it on. It’s plugged in to a 240 plug and the outlet has power. I never noticed an obvious switch to turn it on. Any suggested guidance? Pictures are of the motor and where the power supply comes in to the motor.

Post moved to this page.

Looks like that toggle near the top of the second pic is it.
If the gauges are working, and do not show much or any pressure, moving that should turn it on.
OTOH, if there is considerable pressure in the tank, it may not do anything.
Try opening the drain calve near the bottom of the tank. If air comes out, let it go awhile and the pump may start. If not, try moving the toggle switch. If it still doesn’t turn on, try the steps at:

Come back with what you find out, please.

Thanks Doug for the suggestion. I poked around there but there was no toggle, just a friendly little shock. While I was letting the moisture out of the tank drain, I keep digging around and noticed on the motor itself a little switch that had been painted over that said “reset”. I punched that button and it fired up. It started to build up compression and then I found a unsealed spot down the line. I turned the valve off and powered off the compressor and could hear it hissing. Under the filter of the top most cylinder, where what… Read more »

Save time? Maybe. While the leak there suggests probably both intake and exhaust valves are bad, if the leak is continuous, it suggests a bad check valve at the tank. Looks like you need to remove all the plumbing from the all three heads as well as the curved tube to the tank, anyway. So while that’s off, make sure that check valve is working.Then yeah, you need to pull the head and check the valves in there. BTW, are you telling me that the metal handle sticking out of the upper part of the pressure switch is not a… Read more »

I expect you already know that the threaded rod with the nut circled in the photo is the pressure adjust device for this pressure switch?

I did not know that. I can also see why that could be mistaken as a toggle. It is a spring that is on a piece of long thread, so what you are saying actually makes sense since it has some other mechanical levers and springs attached to it. Added later: I would say the leak from that whole on the top most head is continuous. It continued to leak until there was no longer any compressed air in the tank. Are you saying there is a check valve where the curved tube attaches to the tank? Does a guy… Read more »

(posted again after server problems) “Are you saying there is a check valve where the curved tube attaches to the tank?” Yes. I’m pretty sure the dark blue piece that screws directly into the tank, and to which the curved tube attaches, is a check valve. You’ll want to check that while you have it apart. Regarding a manual, it’s like vehicles – you get a manual for the engine and then the other components like fuel tank, engine operating display, radiators and such are more or less standard or custom built for the vehicle in question. Your machine’s compressor… Read more »

Hello compressor guys, I’m emailing from Scotland. I have an ABAC SPINN rotary compressor, 7.5kw. When I turn it on, it runs at idle OK but then when it tries to load up, the main power at the switchboard is tripped. If I reset the trip, the compressor often runs all day without issue. The electrician says that the trip rating is ample. So there’s something happening when the inlet valve is switching to load? I don’t understand how it’s overloading the motor? I fitted a new motor – but it’s exactly the same? Can someone help me with a… Read more »

Just a SWAG, but I’d guess it’s supposed to be getting lubed at idle, and when you load it, it initially seizes, but gets lube at the same time…so maybe some valve isn’t doing it’s thing. One possibility would be a sticky minimum pressure valve. You should probably have 3-4 bar pressure at idle.

Thanks Doug, I’ll look into that.

I have a Campbell Hausfeld 7.5hp 220v compressor(TF211201AJ). It is 1 year old. The supply wiring is #8awg so it gets good power. It typically runs without issue but last night it ran up to full air capacity, and then I used some air. the pressure switch called for cut-in power and the motor came on for a fraction of a second, then shut off. now it will not restart. The pressure switch has power across it, and continuity. The contactor in the magnetic starter switch box will not make contact and pull in on its own. if i manually depress the contactor, power flow all… Read more »

OK. Before we get into crazy stuff, and given C-H’s troubleshooting tips are pretty generic, I suggest you do the following:
Find a neutral at the power panel.
Measure volts from that to each side of the contactor.
Then, measure across the contactor points.
Report results.

We’ll go from there.

Wow thanks! Got it fixed. I was testing each leg individually to ground. My digital multimeter failed me. It was sensing 120v somehow on a line that was dead! Must have picked up interference from the live side. Your suggestion to test across both helped me figure it out. Tried an analog meter and sure enough, one side dead from the fused safety throwing switch. You are awesome.



You’re welcome.
That sort of thing happens surprisingly frequently. And that’s also one reason why I dislike digital meters…
Thanks for letting us know what it was!

Good morning, I have a Kobalt 37296 26 gallon compressor. From empty, it will run perfectly until there’s about 30 psi, then the breaker switch trips. If I reset it, it runs for a couple seconds, and cuts out again. It doesn’t bog down or change how it sounds, or anything different that I noted. It just cuts out. I have so far only replaced the check valve, but I’m not sure where to go next. I was trying to avoid just throwing parts at it blindly. Any help would be appreciated. Thank you in advance!

Could be a weak breaker. Have you been running it on an extension cord or for over 30 minutes at a time? As a test, you can temporarily jump the contacts on the breaker, and see if there are any problems, like heat or bad smell. If not, replace the breaker. If, on the other hand, it bogs down or otherwise makes funny noises or smells, see if there are capacitors connected to the motor (I don’t know that there are, but typically there would be at least one). Test the capacitor(s). Replace as needed. Let us know what you… Read more »

No, I haven’t been able to run it at all, much less for more than 30 min. It would be from a “cold” start, plugged directly into the wall, several different outlets and buildings. I don’t remember seeing any capacitors on this one, but I’ll look again. I will give that a try and let you know. Thanks for the help!

Good day all, I have a interesting problem for you folks. I’m trying to replace my campbell hausfeld motor that went bad with a lower hp one I had lying around. They are both motor/pump combo units. The original one specs were; 5hp peak 6.5 [email protected] psi 5.1 [email protected] psi 125 max psi Replacement 1.5 running hp 4.8 [email protected] psi 3.5 cfm @ 90 psi 135 max psi The problem that I’m having is the replacement motor runs fine up to 90 psi and then go into lock rotor and kicks the breaker. Up to 90 it runs fine no… Read more »

specs were; 5hp peak

Replacement 1.5 running hp

5HP peak usually translates to maybe 2-3 HP running.
You need a bigger motor or if it’s pulley, a lower “gear” by about x2.

But of the smaller motor/pump combo is rated for 135 psi, should it not pump past 90 psi. I thought it would work but just take longer to fill the tank.

OK. My bad. Missed the motor/pump combo part.
“runs fine up to 90 psi and then go into lock rotor”

If the rotor is locking, the run cap is failing, or possibly there’s a bad winding.

At least by my understanding of “lock”. That means a quick transition from running to stop and probably buzzing.

Sorry for the delay. Finally got the breaker tested with promising results. Replaced it tonight, and it is functioning flawlessly! Thank you very much for the help! It’s very much appreciated.

(You probably meant to say this in your thread, not Scott’s.)

No sweat. Thanks for the update.
Glad to hear it’s working.

Hi I have an old DeVilbiss 330 Air Compressor

B321 co     Ser# B284294
Mod 330    Ser#9603
Max Rpm 800 @ 100# pressure
Max Rpm 800 @150# pressure
Max Rpm 750 @ 200# pressure
Smith way AOsmith corp.
Alt current motor
HP-2 224 1 phase  115/220volts
60 cycle Model # C1224N4AAA
RPM 1725
C rise 40 Type C1
Code J Protector  11701EK ser#
Duty Cont. Amp 23/115
Is there a way to set a higher turn on pressure by adj something. I like to set it at around 100psi auto turn on pressure.

Hard to say. You’ve located the pressure switch. Usually there will be one or two screw adjustments. They will be somehow connected to that spring to raise or lower the tension.
Do you see anything like that?

I have a Speedaire model 5Z702A dual motor compressor. It is fairly new. The problem that I have been having is that sometimes the primary motor can’t restart. It makes an attempt but sounds like a really sluggish and slowed motor. Other times though, it works perfectly fine. The oil level looks perfectly normal and when it runs it sounds perfectly normal. Please help!?

OK, I was writing one thing assuming this is single phase, but it’s three phase, correct? So for starters (pun intended) check all the electric connections between the mains and the primary pump. I suspect you may just have a loose wire somewhere. Also check any relays/contactors for pitting or burning, if visible. Cut the main power first, of course. BTW, does this run primary then secondary with demand, or alternate pumps every start? If you have a manual showing the wiring, please send it.If there’s no drawing, please send some pix of the internal wiring, showing the layout as… Read more »

Last edited 2 years ago by Doug in

I have a relatively new Bostitch compressor 150 Psi Single tank. Are used it a few months ago to fill up a Relatively small pool for the kids. It worked pretty hard to fill it up and towards the end it started to pop and the motor would run and then it would decrease and then come back on and then decrease and come back on and then decrease. It will not fill the tank it will not stay running consistently any suggestionsWould be greatly appreciated. I’m a trim carpenter and I use it with small finish nail guns

Got a model?
Sounds like it might be a brush motor, and they burned out during the long run with the pool..
If you’re lucky, they are replaceable.

Bill, I just replaced the regulator on my Craftsman Pro. Compressor and the valve will control the flow of air.The problem is the gauge only shows full tank pressure and not the amount regulated by the valve. Inlet arrow on the back of the regulator is on the inlet side .
Your help much appreciated., Robert

You either got the wrong regulator, or the gauge is in the wrong hole.
What model is the compressor and the regulator you have in there?

I have a 25 year old oil-lubricated air compressor that I’m repairing. The make is, ICO SRL and is made in Italy. I need to replace about 10 to 15 inches worth of 5/16″ tubing. Can anyone tell me from the pictures I’ve enclose what kind of tubing I would need to use?

Try looking up the DIN or ASTM specs listed on the tube.

I have no idea what DIN or ASTM specs are or where to look them up.


In your middle pic it says DIN followed by a number I can’t make out. Look that up, it has a specific meaning.

I have 5 year old Central Pneumatic 2hp 21 gal oil air compressor. Worked fine for the first few years then started tripping the onboard overload. Called product service, they suggested it was a pressure switch issue. Replaced that and no change. What I have noticed is that it only happens during hot weather. If the ambient tempurature never gets over 80 degrees, it wil run flawlessly. If its over 80 degrees, it will only run for 10 to 15 seconds and trip the switch. Wait a minute or so and repeat. What are your thoughts before I throw it… Read more »

What bridge? I want to catch it.

Seriously, I can’t believe the HFT people steered you to the pressure switch.Ridiculous.

It’s perhaps a long shot, but I’d suspect a thermal expansion problem, hopefully with a capacitor and not the motor windings.
But I don’t know what model you have. Please give the model number.

Meanwhile, checking the capacitor(s) is a thing to do…

hi, i have a 2006 Atlas Copco XAS 97 (JD) the engine starts fine, runs fine as long as i don’t let the start switch fall all the way back to the run position. Starter switch is new. I’ve shorted the wires to the temp. switch, still will not stay running. Wondering what else could cause this???

Engine oil pressure, low fuel?

I have 3/4 tank of diesel, the oil level is full, but I have not checked the oil pressure. I will CK pressure.

Hello Bill, I have a two-head dental air compressor which I use at home as it is so quiet. Unit has run well, but yesterday had to tip it on its back to move it into a new space and after moving it to the new location, and letting it sit on its feet for a while I started it up. Problem is only one head now runs – the other just hums. Each head has its own switch so I just turned the problem one on for a few moments then shut it off. Has been a day and… Read more »

Can you give us a make and model? There’s a few of ’em out there. Failing that a few pix would probably help.

Sure thing, it’s a Copeland Copelamatic KAT4-0100-CABN224, 115v, 1ph. Thanks!

Well, foo. Not finding your exact model, so how ’bout shooting us a pic or three of it? I have an idea what it is, but you know.

How long did you let it sit before you first tried it?
Do you think there’s any chance you knocked something loose as you moved it?
And the other unit started with no apparent problem?
And what the heck – if you’re up for it, could you send a couple of audio files of each one from turn-on to a second or three after. Individually, of course.


Last edited 2 years ago by Doug in

Sure thing. Maybe an hour before turned on. Nothing I can see, and no heavy blow. Yes, the other head starts fine. Almost identical head, but one of them is a replacement I think. Hum is just what you might get from turning on a really old radio. I turn it off immediately. Have tried a few moderate blows with a lead hammer on the casing while switched on, but no effect.

Just guessing here, but there may be capacitors or relays inside the box where the electric cable enters. I’d take the cover off and see if there’s anything fishy going on in there. If there’s a start capacitor, that’d likely be the problem.

I’ll take a look. Doesn’t seem likely that anything electrical will fail just from being tipped over 90º though. I was guessing oil might have flowed in somewhere and created a “lock” of some kind, but no guidance available on something like that? I guess the head comes off next.

Sounds like “slugging” will be the issue from my research, presumably engine oil. Head removal next.

Pulled the head and it is still rotating smoothly, but very slowly and with the humming. Apparently an electrical problem.

Head is off, turns over smoothly, pistons seem good, reed valves look fine. Problem looks to be a capacitor with a broken connection, and water pooling on top.. New capacitor coming up. Looks like a bump while moving was just enough to complete the break.

I don’t suppose you have any idea where that came from? Is the other pump box clean?

No, history uknown, but had some after it left the last dental office, that I know! Haven’t looked in the other box yet. New (spec’d) capacitor fitted today and it started right up. The resistor on the original unit was not on the replacement and is stated to be there to drain the capacitor and prevent shocks when being serviced etc. At least I learned enough to maybe get my junkyard Copeland head set up on a tank. Pulled the plug on the end of the air tank to check it out and interior of the tank appears to have… Read more »

“cleanest compressed air”
I would hope so, as they use it to dry your teeth after suctioning…

“the tank appears to have been coated/painted.” Ditto. It’d be good if all of ’em were.

BTW, does this thing have a vacuum port? I’d guess so, but maybe dentists use a different machine like a reverse blower for that.


Yes, it would be good if they all were, and should be required IMHO, though requiring the walls to be heavier might be a better idea. This is one reason vertical tanks are probably safer: the rust will tend to occur on the bottom “bell” which due to be forged/stamped is probably stronger. Also when such tanks fail catastrophically, they’d be less likely to turn into shrapnel and more likely to try to take off into space. No vacuum port noted.


I have an issue that my compressor will some times start on its own and other times not. I have found that by taking the housing off of the cut out switch. i Can depress the button slowly and it will start effortlessly. Other times like when trying to paint and I’m to far away to throw the switch to off before it lugs and flips the breaker. I’m left holding the gun. So is it the unloader, the switch, or just simply a pain in the…

You’re talking about restarting, then?
Could be the switch, if it has an integrated unloader.
The easiest thing to check is for a leaky/sticky check valve. Inspect and clean or replace. Be careful, it may have a spring that you don’t want to lose.
If that doesn’t help, need a make/model number.

Last edited 2 years ago by Doug in

Yes when restarting but not all the time. mostly I’d say like if it sits for too long before needing to kick on. An hour or so? Not to sure of the individual part names. I have the HF 21gln 2.5 HP 125 PSI

“I have the HF 21gln 2.5 HP 125 PSI”
Sorry, is it a 67847, or another one?
If you don’t have the manual, you can usually get it from HFT, or in some cases, here.

But for now, the check valve is the thing that screws directly into the tank. The discharge tube from the compressor head connects to it, and a small tube goes from it to the pressure switch unloader. It also has what looks kinda like a hex bolt head. The check valve is in there.

This isn’t really a troubleshooting question but not sure the best place to post it. On a new compressor pump, never run, never installed on an air compressor, if I remove the head should I replace the gaskets? The head came off with ease after all the bolts were removed, wasn’t stuck to the gasket, did not need to whack it to get it off. No stick-tion what to ever. The gasket is tight to the valve plate though, can’ t budge it. For all I know they might have used Hi-Tack or something of the like when it was… Read more »

Thanks so much for the last paragraph!

I see no reason to replace that gasket, if none of it came off on the original head, and the new head has the same footprint. If the footprint is a little different, you probably want to re-check the torque a few times over a couple days to be sure the gasket is conforming.

Thanks for the reply. Yeah I figured people be wondering why I’m replacing the head. I did it that way in case I screwed up the head I wouldn’t be left with a big paperweight.

Yes the head is exactly the same, I did install it using the original gaskets. I have a set of gaskets but I figured if they leak I’ll deal with it then, no big deal. I have been checking the bolt torque periodically and the first time or two it did tighten a bit but now it’s not budging.

Cool. And I suppose you know to check again after a few hours of actual operation. Having a spare head and gaskets isn’t a bad thing.

You’re planning to do the original head, too? Might be a good idea to see how the in-service one holds up if there’s any chance it might crack with the bigger outlet.

Last edited 3 years ago by Doug in

My craftsman 15362 pressure builds up. Tank & Tool gages read 100psi. However only a short burst of air comes out. No leaks found and gages stay high. After depressuring tank & recharging, I can get another short burst. Oil is good, hose works on another compressor. Help?!

Note – if you’re looking for parts, this is a 921.153620. Have you tried the hose from the other compressor on this one? And the gauges work, because when you drain the tank, they go to zero? Then most likely either the regulator is bad, or there’s an obstruction between the regulator and the the quick connect. To check, first drain the pressure, then remove the quick connect. Close the drain, turn machine on. Check for air flow from the open end – can you stop it with a finger so pressure builds? If not, you’ve removed the problem. If… Read more »

`fixed it. The quick connect coupler was faulty. Thanks for offering hope anyway!!!

Cool. Thanks for telling is.

My compressor is exhausting air out where the intake filter is. What could cause this? Thank you.

Broken intake valve. It’s what keeps the air in while the piston pushes it into the tank. Or, if you’ve removed the head, it’s assembled backward or upside down.

I’ll have to get some pictures of how it looked when taken apart. Is it possible for some of the air filter foam to have been sucked into the hole above the reed valve ? Could that be the problem? I pulled the head. Turned over. There was filter foam in 1/8″ or so size hole above the reed. So I removed that plate and removed foam from in plate. Then unscrewed the V/U shaped piece as it was stuck under it to

If the foam was holding the valve open, that’s all it takes – it’s effectively broken. But if you got the foam out and the valve isn’t bent up, it should be OK.

Any pictures of the intake valve? I’m a car engine guy. I know what those intake valves look like. Don’t they call all that stuff under that plate the intake valve? Where it is circled is where the green foam was stuck. In the top of the “U”

Well, it depends on where it is. Sometimes the intake and exhaust are the same, others are different. I think the one shown is an intake. Some times the in/out are on the same plate, but looks like this one may have another valve plate for exhaust/out. If you’ve got the manual and/or the make/model it should be fairly apparent which is what/where. If it’s not clear, give model and I can help figure it out (usually).

I have a problem with Iron horse 4.1CFM, 125PSI compressor. I was using it continuously for approx 40 mins (compressor running the entire time), then heard some sparking/ticking sounds from compressor (not sure where exactly), that lasted 5-10 seconds. compressor then started humming without working. There was no smoke.
I have replaced the capacitor, drained the tanks yet it still doesnt work (only buzzes when switched on). I am able to turn the shaft of the motor by hand, so its not seized.

Any other ideas what it could be?

Can’t really read the ID tag, but one other idea is to check for a set of contacts at the back end of the motor – if those are stuck either open or closed, might give this symptom. With the motor stopped, they should be closed. If/when it starts, they should open.

I have searched for these contacts but failed to find them. are you able to direct me to where they could be?

Well, the back end of the motor, near the shaft, if the shaft extends out of the case at all.
Maybe you could send a pic of the back of the motor. It’s possible you’ll need to disassemble it to get to them.
But I’m starting to thing maybe the noise was a motor winding blowing out. Again, probably you need to take it apart to check.
Looks like you can remove some plumbing and get the pump/motor off the base so you can remove the back of the motor.
Good luck.

i am using an IR air winch SWL 1000lbs. and requires 125cfm @ 90psi.

I attached an IR P185 compressor(185cfm @ 100psi) with 30ft of 1″ ID hose and (with that) the winch can only pick 700lbs (measured with scale during test pick).

i tried increasing psi on compressor, bypassed my regulator on the winch, and manually increased rpm.

(Compressor) air filters are a little dirty but not to bad, (no buildup in the fins). what else can i troubleshoot?

How much cable on the drum? If it’s over 1/2 full, then that may be in spec.
Is this a gear or piston unit? Either way, if it stalls and the pressure is good, it’s just reached its limit.

What model is it?

I have a new California air tools ultra quiet air compressor. I am experiencing two issues. #1 There appears to be an air leak where the 1/4 quick fit connector joins to the brass fitting/ collar coming directly off of the compressor. The tubing is 3/8 inches. #2. The plastic tubing that connects from the 3/8 inch tubing to my pneumatic graver keeps on popping off . Both tubing in new and the compressor is new and has not run more than 10 minutes before it pops off, after the compressor has made a cycle and then initiates the next… Read more »

Susan, can you tell us the model number of your machine and/or some pix so we can see just what you have?

I have an older Kobalt 12v/120v inflator I am trying to use to inflate the inner tube I just put into my old walk behind brush hog tire. It’s a brand new conversion from tubeless to tube. The Kobalt says it has reached ( and exceeded pressure) but I can easily still squish the tire down with my hands. Should I believe it? Do I keep filling? The inner tube psi should be no more than 60, but when I set it to 60, it goes well past and then drains down. ??

First off, consider using a pressure gauges to check the tube pressure not just the regulator gauges as the regulator gauges can often be out by a few PSI either way.

When you set what to 60, what goes past, and what drains down please?

Thank you for replying! There is a setting on the front for desired psi, you use up or down arrows and the screen displays your chosen number, you affix the nozel to the valve, the display flashes to zero, you push the on/ pause button and it’s supposed to inflate to that psi and stop. It comes on. It does stop at the desired number, then, more often than not, it displays a much higher number, which you can then enjoy watching drop until it either stabilizes or you disconnect the nosel. There is proper fizzing as if there was… Read more »

The digital regulator is pooched, or the circuit board is. Hope you haven’t had it too long so you can take it back under warranty. Otherwise, I’m guessing you’re out of luck. Sorry.

i have a 25 ? year old speed aire model 3Z355G leaks oil from pulley shaft easy fix ? parts availability ? thanks

If it’s leaking from the actual shaft, your only recourse AFAICT, is try to make a new seal from maybe plastic or rubber.
No parts that I can find, which I’d guess is why you’re here.
If you figure something out, please share.


I have a mcgraw 20gal that’s probably 6-8months old at most(i know….burnt by a harbor freight special…surprise surprise) Thing has run with no issues until about a week ago. Motor will not “turn over” unless the tank is emptied. I called their tech help line and I was told the cold start valve could be the issue. However, my question is: if the cold start valve was jammed, would this prevent the pump from firing up? I understand that it bleeds air for a few seconds before beginning to fill the tank but again i don’t understand how this would… Read more »

A blocked cold start / unloader valve will not stop the pump, but it does overload the motor so that the motor hasn’t the strength to start the compressor pump against the air locked in over the piston. If you dump all the air and it starts, it because doing so also dumps the trapped air over the piston. You need to replace the cold start valve I would think.

Do you hear it unload at shutoff?

I have a Shop Pro 6 gallon 2.5 HP air compressor on two wheels about Three years old.

Four times in one day worked very well like in past three years, next day blows the GFI’s and the breaker on different walls back to
back without “ANY” noise or tick or click or hissss.

Drained the half an ounce of water and the air in the tank filled the oil (was low). NEED YOUR HELP PLEASE.

I’d check/replace the power cord, first off.
If that isn’t it, then the internal wiring might be shorted some-where-how.

good luck
OH, if you need more help, please give the model of your compressor, and/or some pix of it.

I bought an Iron Horse portable air compressor about 2 years ago and it has always performed well. I made the mistake of hooking it up to a long extension cord. I was using a pneumatic stapler and when the compressor kicked on it ran very slow and about 10 seconds later it just stopped. I waited an hour and plugged it into a socket and nothing. just silence. Do you think I burned up the motor? Thank you, Steve

Possibly, Steven. If you only ran it for 10 seconds with too little power, it might not have burned up the motor, but you may have damaged the start capacitor. Follow the troubleshooting tips on this site about air compressors that won’t start, and when you’ve done all the checks and you don’t find anything, check the start capacitor to see if it’s fried.

You might look for a reset button, usually on the motor somewhere, too. There may be a fuse, but we’d need the model number to know.
Do you have the manual for it?

I can hear the engine hum on my air compressor but it will not pump air. I can see the lights dim like it’s using power but the engine just hums.

Jesus, it’s always difficult to provide specific information when we don’t know the make and model of your compressor.

I’ve moved your post to the troubleshooting page on this site, and if you scroll down to the section about compressor starting problems, you’ll find a number of pages that address the issue you have raised.

After reading them, if you still have a question, please add a comment including the make and the model number.