Repair my Emglo AM78-HV4V air compressor

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

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

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

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.

There aren't any brushes in an AC induction motor.

Disconnect the start cap and check both leads for continuity to the plug or mains connection (with it unplugged, of course!) You should see continuity from both cap connections to both line connections, though the (low) resistances will be different. If one of them check open, there's your problem.

The most likely cause is a failed centrifugal start switch.

Hope someone can tell you how to get the motor loose.

Most capacitor start motors have t

Gary,

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

Mike

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

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

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?

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.

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

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).

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.

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

oh come on, mike - a cap costs $5 to $20, just change the stupid thing

- it's almost for sure the problem, and it's cheaper than spend>Gary,

Bill

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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.

Already tried that. Motor starts, but very slowly.

Mike

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

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

Mike