HVAC Air Conditioner DIY repair question

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If you recall, a couple of weeks ago my air conditioner quit working.
With your encouragement, I was able to narrow the problem to a compressor contactor malfunctioning, which caused its coil as well as the 24v transformer primary, to burn out.
I am guessing that it was some sort of obstruction in the contactor that prevented it from fully closing, causing overcurrent in its coil.
I bought replacements for both the contactor, as well as for the transformer, installed both, and everything now seems to work.
I also realized that the outside unit is 9 years old, I did not realize how time flies, I thought that it was much newer.
The repair was relatively easy and instead of paying my HVAC guy (who is all around awesome and honest) $400, my repair cost me only $35.
However, I have a few questions.
1. I was very surprised as to how oxidated was the old contactor. It was borderline disgusting. I would expect that the outside unit would be designed to keep water from dripping on it.
I can buy a heating resistor, to hook it up to incoming 220 volts, something like 5-6 watts (10k ohm) to add heat and drive moisture out of the area. Would such a heater that be a good idea?
2. I saw some mouse droppings there also, which was surprising as that area does not have obvious mouse access. I put some naphthalene based moth balls in there for now to keep animals out. Is there any issue with doing so?
3. Since this kind of stuff seems easy enough, I wonder if I should replace my 9 year old capacitor proactively. Any thoughts on this?
Thanks
i
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Ignoramus24464 wrote:

For the (low) cost of capacitors, I think it makes sense to at least have one on the shelf. When you've got your unit open, you might as well measure the performance of the capacitor with a meter (you have to remove the wires first).
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I just changed the capacitor on my 12 year old Lennox Elite 11 system.
I also replaced the connectors on the ends of the wires. They were loose. One easily slipped off the contactor side when I removed the contactor to burnish the contacts. There was some metal fatigue preventing them from being simply tightened up with a gentle squeeze of the pliers.
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thanks, i agree.
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Ignoramus24464 wrote:

There are contactors that are enclosed and not subject to the elements and other contamination of the contacts. You might look into that. The terminals will still be exposed, but the contacts will not.

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Right, but the replacements are all like this.
i

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On Wed, 13 May 2015 19:28:46 -0500, Ignoramus24464

That's pretty amazing**, but I doubt it will happen again.
**If there were a short in the compressor, the caps, or the fan, that might cause damage to the contactor contacts, but it wouldn't affect the contacor coil. And certainly not the 24 volt transformer.

Great. I wish it were that easy for me!

No.

Nothing wrong with moth balls. The Starship Enterprise had moth balls in its hold to keep space moths from eating the spare uniforms. (When they go out of the ship, even little holes will let the oxygen out,) It also kept away the space mice, but they didn't discuss this. The director's mother was too embarrassed to let the audience know they had mice.

Yes, don't go looking for trouble.
My Carrier compressor lasted about 28 years. I think the capacitor is still good.

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It was not a short in the compressor.
The contactor was unable to close properly. I do industrial stuff and scrap metal and kind of know those things pretty well, usually it happens because a spider makes a nest or some such and there is debris, that prevents the contactor from closing. Or oxidation may make it stuck.
Then the coil experiences overcurrent.
The coil on this was visibly burned.

I was lucky, I guess.
I do industrial stuff and scrap metal and have generally decent understanding of general purpose electricals of such nature.

Why

I hate the smell of mothballs (and so do mice), but outside the home I use them everywhere. They once made their home in my generator control box. I have since then closed the box down and added mothballs.

ok
That's nice to know.
i
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On Thu, 14 May 2015 13:28:38 -0500, Ignoramus19516

I don't understand why the contacts not being able to close would cause over current in the pull in coil for the contactor. There would be a surge current when it first turns on but after that wouldn't the steady state current draw be the same whether it's pulled in or not. Maybe what happened was simply that the coil shorted, that made it draw too much current and that burned out the transformer.

I agree with the "don't go looking for trouble". It seems like there are two kinds of capacitors, the ones that last forever and the ones that go belly up after 3 years. If you have a meter that can test the cap it's worth testing but if it's ok I'd keep it.
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On some contactors the part that pulls in is in the magnetic field and that complets the magnetic flow around the coil. This causes the current to be less than if it was not there.
Not exectally a scientific answere, but something for you to look up if interisted.
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On Thu, 14 May 2015 16:53:12 -0400, "Ralph Mowery"

I went ahead and googled and found http://www.schneider-electric.co.uk/sites/uk/en/support/faqs/faq_main.page?page=content&country=UK&lang=en&id 174800&locale=en_US&redirect=true which seems to support what you say, the idea that if something keeps the contactor from pulling all the way in it will cause higher current due to the "magnetic stuff" as you mentioned.
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You found a great page. They explain what I said in my previous post. Coil current drops when the contactor closes, and if it cannot close, the current would stay high.
i
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Ignoramus19516 wrote:

Eddy currrent when it does not pull to close.
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Ashton Crusher wrote:

When testing cap. ESR meter is good choice.
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On Wed, 13 May 2015 19:28:46 -0500, Ignoramus24464

Speaking from an engineering point of view: Maybe, maybe not.
A high quality oil filled cap may outlast your lifetime and a cheap paper/foil cap that you might replace it with.
Polyester (Mylar) and polypropylene dielectric caps also have a damn near unlimited life. If they fail, its probably due to something like lightening strikes or a motor problem.
Electrolytic caps do have limited life expectancy, so I'd certainly replace that type. They also deteriorate with age, very much more than other dielectric materials. (they are wet inside and the aluminum foil corrodes over time - they can also start to bulge if the can is metal or vent spectacularly if they fail catastrophically)
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wrote:

This begs the question** "How can one tell which knd of cap it is? The first paragraph is usually in a metal can, right?, but what about the 2nd and 3rd paragraphs? All the caps in AC compressors are in metal cans.
**Is this the original use of "begging the question"? It seems to be used slightly differently most of the time these days, in a way that makes less sense.
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wrote:

I think you probably have to develop a feel for it. Oil filled are frequently steel cans with a blob of solder where they were filled and sealed, and then they may be painted. They are probably more rare since they are more expensive. They, and electrolytic, weigh more than Mylar or polypropylene as a rule.
Capacity is an indicator too. Electrolytic put more capacity in a smaller volume as a rule, but voltage rating affects size too.
But you are right, how do you know? When you buy a cap they should tell you what kind it is, but how do you tell what is already in the machine?
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OK, guys, thanks for the enlightening discussion about compressor motor caps. Do I understand it right that if the cap fails, typically the symptom would be a tripped circuit breaker that supplies current to the compressor motor. Right?
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On 5/16/2015 10:35 AM, Ignoramus6769 wrote:

That's one possible symptom. I've usually seen the other one.
- . Christopher A. Young learn more about Jesus . www.lds.org . .
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Which one?
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