Craftsman 2 hp 230v air compressor slows and stalls

by Dave D.

My air compressor starts fine but as the pressure builds the motor slows down an stalls-starst- slows speeds up etc.


After removing the drive belt and starting the motor the motor runs fine (without load)

Is this a capacitor problem or is the capacitor only used to start the motor?

The unit was buit in 1977 so is up ther in age (like me).

Model 919.71752 2hp 60hz 220v 15A

______________________
Bill says...

Hello Dave.

You are correct. The capacitor is used on the motor start up to provide a boost of energy on current inrush so the momentary load doesn't blow the circuit breaker.

The motor is slowing because something in your air circuit is increasing the load. If it speeds up again, then that too-great a load has momentarily disappeared.

What could be causing this is a malfunctioning check valve, one that, as the pressure in the tank builds, creates higher than normal back pressure, increasing motor load.

You might want to log the pressure levels at which the motor speed changes, and test the compressor a number of times to see where the slowing and speeding up occurs.

If it's happening at the same pressure every time, that certainly suggests something mechanical to me.

Add a comment to this post if you wish to discuss this further, after your tests.

Cheers,

Bill

Click here to post comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Craftsman Compressor Issues.

second hand compressor with adjusted pressure switch need to reset it.

by allton
(chicago)

I have a craftsman compressor 921153101 1.5 hp 3 gallon. It is a second hand and the previous owner had adjusted the pressure switch screws. There is a black screw and a metallic screw right below it, can you tell me which one is the cut off and which direction should i turn it to lower it?

thank you very much.

__________________________
Bill says...

Hi Allton, there should be two threaded posts inside the pressure switch, with a nut on them, compressing springs.

One of the springs is for cut out pressure and the level is for cut in.

No, I don't know which is which on your pressure switch.

Drain the tank until the motor starts. Note this pressure level. Close the drain, and wait for the high pressure cut out to occur. Note this pressure level.

Now, adjust one of the nuts a full turn clockwise.

Perform the same test. One of the parameters will have changed, and now you know which nut is which, and which way you have to turn the nut to increase or decrease the set point.

Cheers,

Bill

Click here to post comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Craftsman Compressor Issues.

Pressure is not building up ~ need a manual for my Craftsman Air Compressor

by alex
(camden N.J)

i took of the top of the piston cover for my 125 psi maximum air compressor and i dont know how it goes back together again because it has these two little metal pieces on the top of the piston ring and i dont know how to combine them

_____________________
Bill says...

Hi Alex... I haven't taken your model of compressor apart. I think you may be referring to the valves when you talk about the little metal pieces but I can't be sure.

I've have modified your title to show that you are looking for a manual for your compressor, but since you don't identify the model, it will be hard for anyone with one to know they have it!

You did check with Sears, did you?

Cheers,

Bill

Click here to post comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Craftsman Compressor Issues.

919.167300 - new motor?

by jeff gates
(Lerna,Il)

I have a Craftsman 6hp, 30 gal compressor, 919.167300. Motor is bad. I am trying to decide whether to buy a new on(which is only 1.6hp-all they carry now) or buy a new motor for the old one. $230 for a new motor or $250 for a new compressor with 2 air tools(1.6hp) Advice? Jeff
________________
Jeff, you begin by saying that your compressor is a 6 HP motor. If that is the case, your 1.6 HP motor likely won't even start the compressor.

If it should have said 1.6 HP, try finding any used compressor with the same setup as yours, and swap out motors. I got a used compressor with an excellent motor for $10. The compressor wouldn't build pressure, but that was not related to the motor, but was other issues. The motor was almost new.

Given that - in my Oh so humble opinion - many of the DIY type air compressors are designed as throw-aways, adding a brand new part to an old compressor, particularly when that part is the cost of a new one, doesn't make sense to me.

If the 1.6 HP compressor has enough air flow for your demands, and the replacement motor is the same price, it were me, I'd buy a new compressor and use the old one for parts.

Good luck.

Bill

Comments for 919.167300 - new motor?

Click here to add your own comments

Apr 22, 2012
Craftsman compressor
by: Anonymous

Bill my compressor was a 6hp sears craftsman, 30 gal. I was trying to decide whether to try to buy a 6hp motor and replace it, or buy a new compressor. The new compressors are just 1.6 hp. New 6hp motor $230. New compressor with 1.6 hp motor $250 with 2 nice air tools. Advice?
________________
If you are moving from a 6HP compressor to one with a 1.6HP motor, I suspect you will be very, very disappointed with the flow. Small compressors are best for short blow offs, and to run tools that require bursts of air, like nailers. Any tool that requires continuous flow may not run to your satisfaction when it is being powered by such a small air compressor.

Click here to add your own comments

Add your own question or comment. It's easy to do. How? Simply click here to return to Craftsman Compressor Issues.