Repair my Emglo AM78-HV4V air compressor

[Mike S.]

We were using our Emglo and shut it down for a lunch break. When we came back and tried to start it again all we got was a load electrical hum and sometimes it would pop our 15 amp breaker.

I pulled the compressor/electric motor unit loose from the rest of the compressor so I could get to its guts. When I turned the fan blade by hand (it turned very easily) I could hear the compressor piston working. I even connected the AC power back up but still heard the hum. When I gave the fan a twist the motor started running the compressor. However, the motor won't start the compressor on its own.

I tried a quick test of the start-up capacitor with my multimeter and it appears to be OK. It slowly climbs in ohms until infinity. Reversed the probes and it does the same thing. Sounds like the capacitor is OK to me.

I wanted to pull the electric motor loose from the case so I could see the brushes and rotor. I removed all the mounting screws from everything I could see, but I can't seem to pull the unit apart to get to the motor. Everything is loose and I can twist the case a few degrees, but I can't pull it apart.

Anybody know how I can get the motor out so I can look at its guts. Any help is appreciated. Pretend I'm a dunce and be pretty specific.

Thanks, Mike

[Gary]

Just because a cap doesn't leak at the low voltage provided by a VOM does not mean it isn't leaking at working voltage. Try substituting another cap and see if it helps. My outside air conditioning unit was doing exactly the same thing. Diagnosis: bad starting cap. If your motor uses two caps (one for start, one for run) check the centrufugal switch that controls the caps to see if it is broken. Good luck. 73 Gary

[Grant Erwin]

It's probably still the start cap. Given the relatively low expense of electrolytic capacitors, I'd just replace the start cap and see if that fixes it. My guess is it will.

Take off the "bubble" on the side of the motor and look at the start cap. It may obviously be defective, or maybe you can just get the numbers off it and take them to Grainger or wherever you go to buy a new one. Easy to splice it back in, simple fix. Even if that isn't the problem it won't hurt and it will probably only cost you like $7.

GWE

[Ignoramus26433]

Like others, I cannot think of anything beside the cap.

i

[Bob]

The only thing I can think of is the unloader (if your compressor has one). If it's sticking, there may be too much back pressure, and the motor isn't powerful enough to overcome it.

[Mike S.]

Gary,

Thanks for the input. I'll try to find somebody local that can do a heavy-duty test on this cap.

Mike

[Mike S.]

Hi Grant,

Well, not quite. I've been told by two repair houses that this cap costs $50. I want to make sure it's dead before I replace it.

Thanks, Mike

[Mike S.]

Hi Bob,

Don't think that's the case. When I removed the compressor/motor unit from the rest of the compressor it also removed it from all the air tanks etc. Like I said, spinning the compressor by hand was very easy. Its just that the motor won't start on its own.

Thanks, Mike

[Ignoramus7637]

I am surprised about the cost of caps that you were quoted. They actually should cost a lot less. I have a few start caps that I bought new for like $3 apiece, each about 180 uF. I can sell you a couple for the same price, I have too many. If you arer local to Chicagoland, I can loan you some.

Can you remove belt (if it is a belted compressor) and see if the motor starts by itself without a load?

i

[Robert Bonomi]

That virtually guarantees that the problem is one of two things: 1) stuck/bad (open) centrifugal switch for the start windings on the motor 2) bad start cap.

I'd be tempted to try some 'impact engineering' to see if one can induce the centrifugal switch to close. Proceed at your own risk.

[O D]

If two repair houses told you $50 for the start capacitor then you are being held up with out a gun. Those greedy bastards are not happy with a

100% mark up to sell at $15 then screw them.

[Joseph Gwinn]

Another test is to put a pull rope in the pulley (with no compressor), turn the AC power on, and try to start it like a gasoline engine. Or a RPC without pony motor or caps.

Joe Gwinn

[Ignoramus7637]

Yes, that's a good test, but make sure that all rope is gone off the shaft before you turn AC on (could sound obvious, but needs to be said).

i

[Ken Sterling]

Probably starting switch inside the motor that connects the cap to the windings. Try tapping on the end bell of the motor when you try to start it.... The "points" eventually get a bit pitted and blackened, and typically cleaning them up is all it will need.... HTH Ken.

[Mike Marlow]

Lots easier just to give the pulley a spin by hand.

[Mike S.]

No belt. And when the motor/compressor unit was sitting on the bench it still wouldn't start. If I gave the motor fan a spin and applied power it started to run - although the start up time was very slow.

Mike S.

[Mike S.]

Already tried that. Motor starts, but very slowly.

Mike

[Mike S.]

I'd be glad to check the centrifugal switch - if I knew what it was and where it's located. It's not on my exploded view diagram.

Mike

[Mike S.]

So if that's the case, how do I get to them?

Mike

[Ken Sterling]

Mike, Having trouble finding any kind of info on that particular model - AM78-HV4V...... From your original post, it sounds like this is just a motor, with a pulley, driving a larger pulley via a belt, as you mentioned giving the "fan" a spin. Anyway, ya gotta locate the motor, and take the end bell off to gain access to a centrifugal switch internal to the motor. The switch has a set of contact points on it which close with the motor at rest, putting the cap into the circuit. When the motor starts up, centrifugal force causes the switch to open up and takes the cap out of the circuit until it's needed for the next start. Arcing, pitting, dust, dirt, etc., can keep the contacts from making contact with each other when the motor is at rest. I suggested tapping on the end bell of the motor when trying to start it as sometimes that will let the contacts actually touch each other and get the cap in the circuit to start the motor. That will tell you if the cap is good or not as well as letting you know that the contacts are dirty. I can't see the motor so it's hard to tell you how to take it apart. Sorry. Ken.