Compressor (Sears) Will Not Start

[PabloCruise]

I have an upright Sears compressor, 5 HP, probably about 5 years old, and now when I try to start it, it turns just barely, but then trips a 20 amp breaker.

This is rated for a 15 amp service. I have tried it on multiple 20 amp circuits. The motor turns the compressor maybe an 1/8th of a turn (or less) and then the circuit is tripped.



I have never taken one apart before, and not what I want to do with my Sunday, but I do want to get it running.

Do these things have capacitors in them that could go bad?

Any advice is appreciated!

 

[PAToyota]

First thing to do is remove the belt to see if it is the motor or the pump.

 

[KLF]

^^ what he said.

Then check that the unloader valve is working.

 

[PabloCruise]

You are fast!

I don't think there is a belt, it looks like direct drive.

I can turn over the pump easily by hand, it is not bound up.

 

[PabloCruise]

Then check that the unloader valve is working.

How I do that?

 

[PabloCruise]

^^ what he said.

Then check that the unloader valve is working.

Do you mean the pressure blow-off valve?

I checked the action on that and it was smooth. But while I was at, I opened the tank drain.

The thing fired right up!

So I changed two variables at once, now I don't know which one was the fix! :whoops:

Oh well, at least it started and filled.

Thank you for suggesting that I check blow-off valve!

 

[ducktapeguy]

I believe he means the unloader valve

Unloader Valve

Opening the tank drain has the same effect as the unloader valve, reduces the back pressure on the compressor piston during startup. The valve just does it automatically so you don't have to keep opening and closing the drain everytime it cycles.

 

[PabloCruise]

I believe he means the unloader valve

Unloader Valve

Opening the tank drain has the same effect as the unloader valve, reduces the back pressure on the compressor piston during startup. The valve just does it automatically so you don't have to keep opening and closing the drain everytime it cycles.

Thank you, I will try to find mine and check it out!

 

[se2000]

you might not have one on that compressor. go to sears parts with your model number and find a parts breakdown. There you will see if there is an unloader.
Since it started empty, that is having it unloaded. From being full, Just use enough air and see if it comes on and refills the tank or trips a breaker

 

[PabloCruise]

you might not have one on that compressor. go to sears parts with your model number and find a parts breakdown. There you will see if there is an unloader.
Since it started empty, that is having it unloaded. From being full, Just use enough air and see if it comes on and refills the tank or trips a breaker

Thanks!
I will look for the sears parts website.
I had tried to start it from empty and it kept tripping.
The difference came when I checked the blow-off and tank vent.
Question: if the tank got empty, and then it got cold, my tank could have developed a small vacuum in it, correct? I wonder if that could have been a problem...
I did use some air and the compressor cycled back on a few times, no issues tripping breaker!

 

[se2000]

You would not get enough vacuum.
If it worked after it finally started, I would bet you have a motor problem. Maybe rotating it by hand a bit before starting it will get you a little more life out of it.

 

[PabloCruise]

You would not get enough vacuum.
If it worked after it finally started, I would bet you have a motor problem. Maybe rotating it by hand a bit before starting it will get you a little more life out of it.

Okay, the vacuum was just a theory...

I had been turning it over by hand to see if it was bound up, or of turning the motor do a different spot on the rotor would make a difference, and it never did. It kept tripping.

So I guess the question is; was it just a coincidence that it started after I messed with the blow-off and the tank drain?

 

[se2000]

A motor shop could probably test it for you to make sure but I bet if bad, it won't be worth rebuilding. Probably cheaper to get a new compressor when they go on sale.

 

[PabloCruise]

I believe he means the unloader valve

Unloader Valve

Opening the tank drain has the same effect as the unloader valve, reduces the back pressure on the compressor piston during startup. The valve just does it automatically so you don't have to keep opening and closing the drain everytime it cycles.

This is a good link.

Well all ran well until a few weeks ago when it started tripping again!

So I finally found my manual for Sears model 919.168700

In the troubleshooting it references the check valve, and the pressure release valve (unloader) on the pressure switch.

The manual describes how to clean the check valve, but does not describe how to cycle the pressure release valve. I took the cover off the pressure switch, and that pressure release valve is hidden away pretty well in there...

I guess I will start by cleaning the check valve and go from there.

 

[PabloCruise]

PS: After I took cover off pressure switch and poked around in there, compressor did fire right up.

It sounds like the relationship between Check Valve and Pressure Release Valve is such that I should start by cleaning Check Valve, as I have never done this.

Also, the manual calls this model "Permanently Lubricated" but I did hear the cylinder squeaking when i rotated by hand, so I shot a little WD-40 in there and it spins much easier now. Good idea? Bad idea? Meh?

Thanks

 

[PabloCruise]

PPS: If it comes down to needing a new Pressure Release Valve for this unit, am I stuck going to Sears for a Craftsman replacement? Or is there another source for bolt-in replacement?

Thanks!

 

[PabloCruise]

Finally got some time to mess with this, it has been bugging me.

I took the Check Valve (# 27) in above diagram out and cleaned it with degreaser and brake cleaner.

I blew into it and you can blow through it.

I took the tank drain valve completely off and left it off so the tank is at atmospheric pressure.

Put the check valve back together (left tank drain valve off) - still trips breaker.

Manual says that the Valve Plate Assembly (intake and exhaust valves of compressor piston) should be "checked" by a trained service technician. It does not say checked for what... So I pulled the head and pulled the plate. It has metal reeds that flap open or closed in response to pressure.

I rotated the cylinder sleeve 90 degrees, wiped it out and put some air tool oil on the cylinder wall and put it all back together w/ the piston at TDC, so there absolutely cannot be any head pressure on the piston/pump. The tank drain valve is still off.

I flipped the switch, the motor made probably a few revolutions and then ceased. 20 amp breaker is tripped.

So at this point I am wondering if the pressure switch is defective? Or if the starting capacitor is bad? Can they be bad and still spin the motor for a few initial revolutions?

Help...

 

[PabloCruise]

Now that I think on this a little more, I am thinking it would have to be the starting capacitor.

If the pressure switch were bad, it would simply shut the motor off before the desired pressure were reached, yes?

But instead, the breaker trips.

Anyone?

 

[PabloCruise]

Well, I'll keep y'all posted as to how I make out with this.

 

[zebrabeefj40]

My folks have a similar compressor and had the motor itself fail. IIRC there is a known issue with that design motor burning up windings and acting just like yours is. I do not know how to test it as my brother is the electrical wiz; an electric motor shop could tell you in less than 5 minutes if the motor is bad or not. Sears was the only source of the motor because one endbell is also the compressor mount.

Nick