I have a small portable (electric) air compressor. If I start it up with no pressure in the tank, it runs fine and fills the tank with air like its supposed to. But if there's any air pressure already in the tank, the motor will not start, and I can't refill the air tank. If I release all of the pressure out of the tank manually and restart it, the motor will run fine and refills the tank. Any ideas?

First, welcome to the Pool. You will find that it is a great place to hang out.

While I can not address your particular Craftsman product, I can give you a couple of items to check.

Most compressors can not start with a full head of pressure. They should have a start unloader of some sort and a check valve between the compressor and the holding tank. The unloader relieves the pressure off the pistons and the check valve only allows air to flow in one direction, towards the tank.

When the compressor stops, the unloader will open allowing the air pressure to drop on the pistons and the check valve will close keeping the tank air from escaping through the unloader.

If the check valve is stuck open, then the compressor is trying to start with a full head of air. You may also note that the air pressure in the tank may be going down faster then normal when not in use.

Follow the lines from the compressor to the tank and you should be able to locate these items. Be careful as parts under pressure can and will blow off with great force even though you think the pressure is low. If you hear any air escaping while removing parts, wait until the sound stops and then remove slowly.

If this is of no help, you may have a bad motor that will not develop enough starting torque to over come starting pressure but runs fine once it gets going.

If you have a Sears/Craftsman model number, that may help if I can find a service manual on line. Check your manual if you have it. Sears/Craftsman are good about having all the information packed with the unit including a parts list.

Again, this is general and may not apply to you unit.

PS. I am adding this after checking my Craftsman compressor. The compressor may have a bad discharge reed valve.

There are 2 types of reed valves for each cylinder. As the piston goes down, the intake reed valve opens to let air into the cylinder. As the pisoton goes up and compresses the air, the discharge reed valve opens when the pressure is equal to the the tank pressure.

If this reed valve is damaged, it will allow tank pressure back into the cylinder. This would act the same as a bad check valve.

This is a simple repair on my unit.

This message has been edited. Last edited by: Walks On Water,

I think I solved the problem. All of the valves were functioning and the bleed off valve released the head pressure with no problem. Believe it or not, the problem was that I was using an extension cord. I re-read the instructions and they recommend use of no extension cord, or a 12 gage or larger cord if one must be used. I was using a 16 gage 50' cord. The loss of voltage was enough to not give the compressor enouigh juice to power itself up. I retried it without the cord, and it works perfectly! Thanks for the advice.

It's funny.

We always overlook the obvious.

I have a Craftsman air compressor that just went out this afternoon. We heard a little click at about 80 psi and then the pressure started dropping. The reeds that you mentioned seem to just float in the region of the valves. Is that normal? It seems strange that they are not attached in some what to the surface. I put it back together and the pressure will come up to 30lbs and then the compressor just runs, but no more pressure. Any thoughts?

The reed valves do "Just Float" over their openings on the intake side. In most compressors, the discharge valves have spring helpers.

Not knowing your unit, I would suggest you check Sears on-line parts center and look at the diagrams there for your unit.

Sears Parts

One thing I have found is the discharge tube from the compressor is just held in place with a rubber gasket on some units. This becomes dry and lets air excape and not letting it build up pressure.

Hope this helps and welcome to the pool.

Thanks for the info. I went a bit further in taking the unit apart and found that there is a gasket on the intake to compressor face of the system. The center part of the gasket that splits the intake from the compressor side had blown out. Since I was working on a car, I took part of one of the old gaskets from the car and put it in the bridged region for a short-term fix and it worked.

I still need to get a new gasket, but it has been interesting learning a bit about how the unit works. Thanks again, Bill

I have a brand new Sears 1.6 HP 26 Gallon Electric compressor. I had only used it a few times but the bleeder valve at the bottom has been a problem that has only gotten worse. First it was difficult to bleed anything out of it no matter how far I turned it. The suddenly it would work. Now it bleeds all of the time and I can not get any pressure above 30 PSI. I was thinking of putting some teflon tape on it but that might invalidate my warranty. Ideas are most welcome.

waniac - if it's brand new is there a reason you haven't taken it back to the store? Even if you didn't get an extended warranty, there should be a basic warranty on it. If it hasn't been too long, they'd probably just replace it, or at least repair it.

Oh, and definitely do not try to jerry-rig it, any modifications would definitely invalidate your warranty.

first i would drain all the air out then i would remave the darn valve then i would go vist my local hardware store with valve in hand and ask them if the got a better valve maybe an elbow if needed to move it out to where you can get to it better. there are some good brass valves like a gas valve(as in propane) simple one lever jobbers. those valves that come on fatory stuff is junk.

Hello new here,,,i am also having the same problem with the practicaly new air compressor from sears the model number is 921.166400 i will try the power cord thing,it looks i i did not read it or i forgot,,,been using a long cord also.Just hope the motor is ok as it turns on but it does not pass the 30 lbs of pressure.Glad i gound the this site,,,seems like a real cool one.Any help if the power cord trick doesnt work will gladly be appreciated.I will post if the cord was the trick,,,but it will be tomorrow due to the time here.Thanks again.
Bruno

welcome brunop39 too the pool

I have a Craftsman model 919.168700 33 gal. upright air compressor that has worked great for a couple of years now. Just yesterday, I turn it on as I always have and it acts like it wants to start (kind of sounds like an idling Harley Davidson!) and then trips the breaker. I've tried to research this and have seen people with similar problems suggest checking the following: check valve, unloader valve, run capacitor, and capacitor centrifugal switch. I've also seen some say that Sears will not sell you parts--only a new motor. I also found out that I should not have been using an extension cord--which I have been for two+ years.

Any advice on what I should check/replace first? How will I know if it is good or bad? Will I just need to replace parts until it works again? If so, where can I order parts? Thanks so much for any help.

Brad

Sears is right in not selling motor parts as they don't know how handy the buyers are.

Your best bet is the new motor and while your at it, a heavey duty extension cord if really needed.

While pulling, let's say, 10 amps through a 6ft # 14 wire cord would be OK by the time you pull that same 10 amps at 120 volts down a 20ft cord could really put a strain on the motor as it may not have enough volts to start properly.

Then add the wire from your breaker panel to the outlet and now how far have you run?