Compressor / mag motor control issues

[Colohusker]

Okay, I picked up a Dresser 5HP/80 Gallon compressor last year, and it's been working great, but last weekend I turned it on and it seemed like something was caught in the motor, it would turn for a millisecond, then stop, then turn again and just try to freeze up but eventually run okay.

I finally had time to look at it today due to the snow, and I think the issue is the magnetic motor starter/control. I took the guards off, motor spins by hand easily with no belts on it, but same behavior when I flip the breaker. When I watch it, there is a ton of arcing coming from the magnetic motor control, so I think the contacts need cleaned or the coil replaced.

But, I'm a novice when working with these type of controls, so looking for help. Is it possible to clean the contacts, and if so how would I do it? Same thing for checking or replacing the coil?

The motor control is a GE CR354AC, and I've attached some pictures if it helps.

Thanks in advance for any suggestions or instructions!

Scott

 

[67Dart273]

Essentially what you have there is a big relay, a contactor, with a protector device below.

If the contacts are arcing, it could be the

contacts

something wrong in the motor itself

a bad start capacitor

or the unloader may not be working.

What do you have for an unloader? Some are supposed to be automatic, are self contained in the check valve

Some are a separate tube going to a little mechanical valve on the pressure switch

Others are a mechanical device right on the compressor.

When it stops, you should hear the hiss of air being released off the head.

When you say it "turns freely" does it seem like there is compression, or does it seem like the compression is released?

I'd concentrate on the unloader, because to me, this sounds like "what it's doing"

If that seems OK, I'd first kill the power to the starter box, and you can take the front cover off and inspect the contacts. BE CAREFUL of springs/ parts falling out when you do so.

It is NORMAL for contacts to show a certain amount of pitting and burning. IF possible, post a photo of 'em here

If they don't look too bad, I'd replace the start cap.

 

[Colohusker]

Okay, here are the pictures of the contacts, and they look pretty pitted to me so I'm going to take an emery board and clean them up and see.

The unloader is built in to the pressure switch, so when power is turned off a valve opens.

As far as spinning freely, I was referring to the motor by itself. I took the belts off since they need replaced anyways. On the pump, I can turn it and feel the compression as it turns.

At this point, I'm thinking the contacts just need to be cleaned, but if it still arcs I'm thinking either a loose connection from the pressure switch to the coil, a faulty pressure switch that is going on and off, or a faulty coil. What it acts like is the magnet is pulling the contacts open and closed instead of holding them closed, and from the amount of pitting on the contacts that looks to be the case so we'll go from here.

Thanks for the suggestions of things to look at! Now that I have it apart I see that it is like a relay on steriods and understand it better.

Scott

 

[67Dart273]

I would almost bet it is NOT the contacts.

You can do more damage with trying to clean them "than not" by removing the coating on the contacts

BEFORE you decide to mess with the contacts, try this:

Pull the power to this disconnect, and make yourself two no12 jumper wires about a foot long with ring terminals, and simply bypass the contactor with your jumper wires, left side top to bottom, and right side top to bottom


Then turn the disconnect/ breaker back on and see if you temporarily "cured" the problem.

I'm betting you did not.

 

[Colohusker]

Thanks, I'll give that a try. Once I cleaned the contacts with some electronics cleaner, they didn't look too bad so just put them in and the issue persists. So, if bypassing the contactor has the same issue, would it be the cap on the motor? If bypassing does get rid of the issue, would it be the coil?

Thanks again for the help!

 

[67Dart273]

It might be the cap on the motor, but I'm still thinking compression release.

It also could be something wrong in the motor, bad start switch or bad start winding.

The coils in those contactors are almost always either good or bad, so if it pulls the contactor in, and does not heat up (smoke) the coil should be OK

One thing that DOES happen to contactors, due to excessive use, cycling, dirt, or other foreign objects inside the thing, sometimes the plunger/ armature of the contactor no longer seats properly. Usually, they "buzz" excessively when this happens.

Usually, if you take the trouble to take it apart, you can see obviious wear on the parts of the contactor.

If bypassing the contactor does not clear the trouble, I'd take a REAL good look at the compression release.

If that leads nowhere, I"d replace the start cap because they don't cost much.

If you get to the point that you are sure the compression release is OK, replaced the cap, and bypassed the contactor, if you feel up to it, inspect the start switch in the motor, and if not take it to a rebuilder for testing. If you get into the motor, visually inspect the windings carefully for smell and signs of charring/ burning

If the start switch seems OK, then it's time to go to the rebuilder for testing the windings. A GOOD motor rebuilder can check the windings for not much money.

 

[Colohusker]

Thanks for all the suggestions. I bypassed the contactors, and the issue went away and the motor ran smoothly but there was still a loud ticking. I still had the coil in the circuit and I could hear it opening and closing the contactors that was causing the ticking.

I then disconnected the coil leads and it just hums along like it should with the contactors bypassed and the coil disconnected with no ticking.

Thinking it might be the pressure switch since that activates the coil, I bypassed that and put the coil back active and it was opening and closing about once a second with the ticking.

I didn't see any obvious wear signs when I had it apart. Is there any way to test the coil with a voltmeter?

Thanks,
Scott

 

[67Dart273]

THAT sounds like the motor protector, the device below the contactor, is trying to drop the motor off line. I'd say it's time to get some help. Do you have a friend who's an electrician, a millwright, or an HVAC/ refrigeration tech? Someone with a clamp--on AC ammeter who can measure motor draw and so on?

 

[Colohusker]

No, but I'll probably give a mobile compressor service outfit a call and have them come and take a look at it. Rather spend a couple of hundred on a service call instead of risking the motor and replacing that at $600 or more.

Thanks again for all the assistance!

 

[67Dart273]

Post back, will ya---and let us know what it turns out to be. ---- and good luck

 

[Colohusker]

Okay, took it apart again to look at the control section of it, didn't see anything corroded or looking out of place, but did notice from the design that the plastic carrier that controls the switch moved really easy. Since we were supposed to be moving shortly after I got the compressor, I mounted the control on the frame of the compressor to save some hassle in moving it. Just to see what would happen, I moved it and mounted the control box to the wall next to it thinking maybe the vibration on startup was causing the plastic carrier to bounce making the switch open and close. After I moved it and got everything wired back up, viola, no more issues. Starts right up without the on and off behavior and hums right along.

Thanks for your suggestions and help! I don't think I would have had the courage to take it apart and figure out how it works without your advice and encouragement.

 

[67Dart273]

Oh, WOW. So I guess the vibration of the pump was bouncing the contactor around? Weird.

Glad you got 'er fixed.

 

[green1]

Strange, usually if contacts get corroded, they take out the relay contacts in the end of the motor with them. Never heard of vibration doing that.