Outside air conditioner unit blew circuit breaker, sparked ...


So, last week, we found that the air conditioner wasn't working. The inside blower was working, but it was blowing room-temperature air.
I tracked the problem down to the big (50 A) circuit breaker being blown. I switched it back, and it immediately blew again (well, in about a second) and I heard a noise from the outside A/C unit (on the other side of the house, so I couldn't see it.)
So I got my wife to do the circuit breaker again while I was watching the outside unit. The motor glowed or sparked or something -- light came out. I wasn't that close, so I'm not sure exactly which. I'm also note sure what the fan did.
It was raining, so I left things off, went inside.
I came back out the next day, sunny skies, and tried it again, this time being close to the unit so I could see exactly what happened. And it started up fine, no problems. Turning it off again, I saw that the fan spun pretty freely -- it doesn't seem to have problems with the bearings (as I've had in other appliances.)
So now it seems fine. But I'm reluctant to actually turn it on. Yes, the circuit breakers will protect me from future problems, but I don't like relying on it.
I'm not much of a handyman, but I could replace the motor and/or condensor easily enough -- it's easily accessible. And of course I'll have everything off and the circuit breaker off if I try. This is about 10 years old, and living in Texas, it gets a lot of use.
But should I? Or should I just check that water isn't getting in somewhere?
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Doug McLaren, snipped-for-privacy@frenzied.us

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If it coughs when raining and works when dry, I would definitely suspect a water intrusion issue. However you may want to have an HVAC guy look at it anyway - a 50A, 240VAC circuit can knock you back a bit if you're not careful. Depends on your comfort level working with this stuff.
nate
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N8N wrote:

Rather that "comfort level" it might have been better to write "knowledge and experience".
Fools rush in where......
Jeff
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| > If it coughs when raining and works when dry, I would definitely | > suspect a water intrusion issue. However you may want to have an HVAC | > guy look at it anyway - a 50A, 240VAC circuit can knock you back a bit | > if you're not careful. Depends on your comfort level working with | > this stuff. | | Rather that "comfort level" it might have been better to write | "knowledge and experience". | | Fools rush in where......
Anything I do, the A/C will be off, the circuit breaker will be off, and the switch near the outside unit will be off before I go near the thing.
I'm not an electrician, but I know that much :)
A condensor is just a capicator, and it can store voltage as well, though being connected directly to the wirings of a motor I wouldn't expect it to store anything more than a second. But I'll short it out with an insulated screwdriver before I touch it just to be sure.
I'll also check for voltage with a multimeter in HV mode before I touch anything. I really wouldn't expect any, but I'll check.
And I'll try to work with one hand in my pocket, just in case.
I think that covers all the electrical safety issues.
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Doug McLaren, snipped-for-privacy@frenzied.us
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It is probably not the fan. It's probably the compressor. I'm thinking you can't replace the compressor because you probably do not have a recovery system and an oxy/acetylene set to braze the new one in. But you could surprise me I suppose.
Be careful even messing around with the wire terminals at the compressor. Turned off it still has at min of 100 psi pressure inside it. Sometimes those terminals get old and will blow out the side when you start messing around wth them.
The compressor takes a whole lot of current to start up. There are hard start kits that can be added to ones that have trouble starting. You orbably ought to get an hvac guy to look at it. He can put a clamp meter on it and see how much current it is drawing on start up.
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| It is probably not the fan. It's probably the compressor. I'm | thinking you can't replace the compressor because you probably do not | have a recovery system and an oxy/acetylene set to braze the new one | in. But you could surprise me I suppose.
I will not be attempting to replace the compressor myself. The outside fan, that's easy to get to and I'd try it myself. If it is the compressor, I'll pay a professional for that.
But in this case, sparks (or just light -- I'm not sure what) came from the outside unit when it started, seemingly from the motor. The outside unit seems to be just a fan surrounded by a radiator. (I'm guessing the compressor is inside.) I wasn't close when it happened -- but I did see it light up (it was night time, so I could see it) -- which tells me something either emitted sparks, or got red hot before the circuit breaker blew again.
As I understand it, it's a three phase motor but powered by one phase power, and the condensor helps this arrangement work. If a motor can't start, it'll draw a massive amount of current and get hot, fast. My theory is that the condensor wasn't working properly and so the motor couldn't start, the winds got red hot in a second before it the breaker blew. But it's just a theory -- I've little actual experience with this motor/condensor setup, though I am somewhat familiar with DC motors. The motor seems to spin freely.
I only have one case of failure to work with, but I'm guessing that the condensor got wet and that prevented it from working properly so it couldn't help the motor start. My current plan is to clean the condensor off, make sure it's all waterproof, and then run with it. I guess since the motor is outside, with nothing flammable nearby, and it does have an effective breaker, there's little actual risk of fire -- at most, it'll fry the motor.
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On Oct 27, 5:10pm, "Doug McLaren" <dougmc

I don;t know what you're looking at or talking about, but all the residential compressors that I have seen have compressors where the motor is sealed inside with the refrigerant. It's like a sealed refrigerator motor. So, you couldn't see fire or sparks from the compressor motor. It would have to be an external component, ie relay, starting capacitor, etc, or the wires where they enter the compressor, etc. Also, if the windings on any motor got "red hot", then the motor is kaput. It's possible the flash was from the fan motor.
Also, I would not rely on the breaker giving you protection from a bad outcome. For example, if something is partially corroded, not making contact, it could develop enough resistance and generate heat, starting a fire, without ever tripping the breaker. Or if the unit is not properly grounded, a partial short could leave the case hot, etc.
You could do a thorough inspection and you may find the obvious culprit. With it arcing, one would think it wouldn't be too hard to track down by visual or smell.

All the capacitors I've seen could have water poured on them and still would not matter. They are sealed.
I

Probably, as long as there are no flamable items there now or in the future. I've seen units with plenty of leaves in them and nearby.
Bottom line, I'd make sure I found out exactly what caused this.
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Not making fun of you, but quit calling the capacitor a condenser. Especially when talking about air condioners. I don't recall any calling a capacitor a condenser in many years and I deal with electrical and electronics every day. A condenser is usually though of as a part where the refergent goes through.
The motor is not three phase either. It may be a single phase with a capacitor start. The capacitor does help it start up.
YOu probably have a fan motor and the compressor will have another motor inside it. That motor is not replaceable except for the whole compressor.
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Is that a Trane unit? I have seen quite a few Tranes where the cranckcase heater shorts out-- and it seems to happen a lot more often with heavy rain. If so, it is a fairly easy and inexpensive repair. Larry
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They're still commonly referred to as condensers in an automotive context. Not sure why...
nate
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N8N wrote:

Should have seen the guys at the NAPA store back in '79' when I, fresh out of electronics school, asked for points and a capacitor. I left there with the right parts, but they were still standing firm that the part I bought was a condenser and NOT a capacitor.
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I thought condensors were how cows put milk in them little cans?
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Tony wrote:

Semantics. When I was working overseas there was this crotchety old Marine who was the construction superintendent and the guy kept yelling about a "flat rack". It turned out to be a "flat bed truck".
TDD
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On Oct 27, 5:10pm, "Doug McLaren" <dougmc

The flash you saw may have been normal. The fan and compressor are both started by a large relay. Depending on where it is located and how well all the covers are installed it is possible you saw it arcing when it tried to start the unit. The relay has open contacts so it is possible to see a flash in the dark.
Both the fan motor and the compressor motor will have capacitors, aka condensors. If both are now running then the capacitors are most likely good. They tend to fail competely and when they do the motor in question doesn't run. The fan also tends to fail completely and is obviously failed when it won't run. Since your is running odds are it is good. The relay is a dual pole with both hots running through it. It is pulled by a 24vac power over a small line form the air hanlder. The fan motor is 120, the compressor is 240. The compressor motor and the actual compressor it's self are sealed inside a big roundish can in the middle of the unit. The can is two halves welded together so the compressor motor is not servicable.
The compressor can become hard to start. It has to start under a load even normally because the refrigerant is already at a significant pressure. Various problem situations can also cause the refrigerant to enter the compressor in a liquid state and then it really has a hard time starting. Those problems can come and go based on outside/ inside temps and what the inside airhandler is doing. So the fact that it appears to be working fine now is not an indication of clear sailing. The compressor also has a overheat/overload safety device in it. That too is not servicable. If the compressor is having too much trouble starting that will kick out. You don't want to keep causing that ovcerload to kick as it will get weak just like letting a breaker pop over and over.
You can certainly look around inside with the service cutoff turned off. But you really need someone with some equipment; guages, clamp on current meter, thermometer to take a look at. A good service tech will check the pressures, temps outside and inside, as well as the compressor start up and run current.
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So, are you saying the outside unit is working OK, and producing cold air from the evaporator coil on the furnace? If so, I doubt there is an internal compressor problem since that is a sealed unit. It is either a problem with the wiring to the cooling fan motor or perhaps the relay unit that applies full line AC power to the compressor and to the cooling fan when the thermostat calls for cooling. The compressor is most likely across the full line to line, 240 V. The cooling fan is most likely 120V, one line to ground. No home unit is three-phase like an earlier poster suggested, unless you live in a multimillion dollar mansion in which case yhou most likely would not be doing it yourself.
With power fully turned off, check the insulation where power goes into the compressor to make sure it is ok. Then look carefully at the pwer into the cooling fan and also all connections to the power control relay. If you saw sparks, there must be someplace where the insulation around the wires will be discolored.
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Doug McLaren wrote:

Definitely remove the side panels and look for arcing, bare wires or anything else that's obvious.
It MAY be something trivial!
It could very well be that a mouse tried to get out of the rain then tried to dry himself by draping his body over the warm power relay...
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dougmc+ snipped-for-privacy@frenzied.us (Doug McLaren) says...

Chances are a mouse looking for a warm spot shorted out some contacts. After he fried for a while, the problem cleared. A lonely raccoon took down a whole substation that way last winter. You should attack the unit with a whisk broom and an air compressor before calling for service.
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