Old one cylinder oiless tankless air compresser.

If the motor was turning the compressor ok, then it may not be a bad motor. I would suspect a broken reed valve.

Is the motor still turning the compressor? If not, will the motor run if you slip the belt off the compressor?

A bad start/run capacitor can prevent a motor from starting up, and if it does start with no load, it may not generate any power.

Exactly what I was thinking...Or a crack or hole in the piston or at least something internal.

When it started acting up, I unplugged it and I tried two more times.Each time, it started with the usual normal knocking noise for a few seconds when I put the air hose chuck on the tire stem, then a few seconds later, the unusual soft thumping noise.There is a shop/store about five miles from me which sells and services electric motor powered equipment.I reckon next week I will take it over over there and let them check it out.If it is only the capacitor, I can buy a new one there, or at the Johnstone store a few miles from me.It is a very heavy, heavy duty small air compresser.It must weigh about forty or fifty pounds, at least.It almost turns me over when I pick it up. cuhulin

I guess this doesnt have an external motor with belt drive? If it is a sealed unit system, then you may not have any other thing that can be fixed except trying the capacitor.

My first thought would be that the reed (or caged ball, or whatever flavor it has) valve has died - whether it failed open or closed is pretty well irrelevant, the result will be the same. Following that would be a guess that the connecting rod "isn't" anymore - either it broke, the pivot pin on one end or the other let go, or similar.

Had an old plug-it-into-the-cigarette-lighter version of one of these things - slow, but effective if you're stuck out in the backside of beyond with a flat, useless for much of anything else. It died a couple months ago. When I pulled it apart, I found that the folded piece of strap metal that passed for a connecting rod had worn through at the piston end - It still seemed to make all the right noises, from the slapping of the broken end, but it didn't move any air.

Capacitor is used as an aid in starting. Once the motor is turning it has no affect.

Another oiless tankless 120 volts air compresser I own is a light weight Speed Aire, made by Campbell Hausfeld company.It runs, but doesn't pump air pressure.I think the reeds are worn down too much.It dates back to the 1970s.

I own two 12 volt air compressers which plug into a cigarette lighter, I hardly ever use them because they are so slow pumping up tires.I keep one of them in my 1978 Dodge van and the other one in my 1983 Dodge van, just in case. cuhulin

That depends upon the motor... A RUN capacitor is engaged all the time on some motors. A START capacitor may be required, as you say, to start motors under load. Whatever the case, replacement of the capacitor(s) is a fairly common situation and can be fairly inexpensive, compared to calling out an electrician or buying a new unitl.

One day next week, I will take my old heavy (I weighed it, it weighs 44 pounds) air compresser to the electric shop and let them check out the capacitor.In fact, I will also take my Speed Aire light weight air compresser too, and ask them if they have new reeds, or can they order them for me.

If no luck, I will go to the Sears store and the Lowe's store and the Grainger store and see what they have.

Yesterday, I received a snail mail from Motor Trend.One year snail mail subscription for $10.00.I sent them a check for $10.00. cuhulin

I dont read them nearly as much as I would like to anymore. If you read enough, sometime you will get a smattering of the truth.

A lot of these magazines are just cheerleaders for anything fast, new, pretty, or politically correct. When the new wears off the car, then you will know whether it was a good buy, or whether you will hate it as long as you own it.

Have had both experiences.

Based on the symptoms you describe, it CAN'T be the capacitor. You report that the motor is spinning up, and continues to spin, but the machine isn't moving any air. Which isolates the problem to the pump side of things.

If the motor didn't run AT ALL, or spun up then stopped completely as soon as it hit any kind of load, THEN you'd be smart to look at a bad capacitor or other problem with the motor. What you've described so far completely rules out that possibility - if it were a bad run capacitor, the motor MIGHT spin up, but would die almost instantly under even a light load. If it were a bad start capacitor, it wouldn't even try to spin up to begin with.

Since you say it starts and continues to run, even though it doesn't move air like it's supposed to, that eliminates the possibility of it being a problem with the motor - regardless of whether or not it uses a capacitor (doesn't matter if it's a start or run type) at all.

If you want to bring it back to life, you should be concentrating on, in order of likelihood, the valve(s), the connecting rod and/or its associated connections to the motor shaft and piston, the piston rings (if it has them), the piston itself, or the cylinder.

Thanks hls. Will have to read up on that.

It is a rainy day here today, not much I can do outside.I think I will start tearing into my old heavy air compressor right now, although I doubt if new parts are available for such an old air compressor.

I was mistaken about something concerning my Speed Aire light weight air compressor.I just now looked at the label on it.It says, Speed Aire MFG.FOR DAYTON ELECTRIC MFG.CO.CHICAGO 60648 U.S.A.

The motor is 3/4 horsepower, 125 psi.I guess it wasen't made by Campbell Hausfeld. cuhulin

I reckon I sort of kind of fixed my old heavy air compressor, for a while anyway.Two problems, a broken reed and two small cracks in the rubber diaphram ring mounted between the top of the cylinder and the top of the inside of the cylinder wall.I snugged the good end of the reed under one of the screws, one of the two small screws which holds a rigid metal piece above the reed, that piece fits over the reed.Then I put all the parts back together and I tried it out.It aired that old tire up just fine.

I have a lot of very old electric clocks and wind up clocks.At least one of them has a broken main spring.If the broken clock main spring is wide enough, next time my old heavy air compressor starts acting up, I think I can use my tin snips and cut a new reed. There is always more than one way to skin a cat. cuhulin