A/C problem, need help ASAP

[Ignoramus2645]

I am giving about 60% that I can diagnose it tonight.

i

[Ignoramus2645]

Good idea, I will check motor leads for leaks to ground. (the main motor leads should read a very low resistance to one another).

i

[Pete C.]

It's also rather sad that the protective devices are "optional" or "accessories".

Pete C.

[DoN. Nichols]

According to Ignoramus2645 :

That -- or the main motor itself.

Note that any air conditioning compressor *must* be allowed to rest for a certain number of seconds (sometimes low minutes) before power is re-applied. There is normally a timer which prevents re-application of power until this time has elapsed. (The problem being that the compressor cannot start in the face of the pressure differential which existed while it was running.)

I had one such delay timer fail -- but it failed in the "never try to start" mode, and I was able to swap in a similar unit to put the system back in service myself.

Some air conditioner systems, at least, have a solenoid valve to speed up the bleed-back and shorten the time before it can be restarted.

I *suspect* that what has happened is that the nearby lightning strikes zapped the timer module, and re-applied power to the compressor immediately after it stopped -- a condition under which it *can't* re-start.

I have seen (where I used to work) large industrial air conditioning units without such a delay working blow up and squirt Freon out the door for about thirty seconds. I believe that a connecting rod in the pump failed in that case. I was in my car in the parking lot relaxing during lunch when I saw it happen. Luckily, there were two other units which survived and kept running, so we were not baked out of our labs.

Anyway -- I suspect physical damage to the compressor, rather than something as simple as a failed capacitor. And from your description, it sounds as though the motor is cap-start/cap-run. The motor *might* have developed a short on the capacitor-fed winding during the attempted too-soon restart.

I also suspect that both sections of the capacitor are of similar values, so you could try substituting the other section in for a quick test.

I don't think that they would have anything connected to the can at these voltages, so there should be a common terminal.

Do you have a capacitance meter to try on the capacitor?

You have some guesses, at least. I'm afraid that you will need a new compressor unit, and a professional to replace it, unless you have access to the refrigerant as well as having a charging manifold. (Given your questions, I suspect that you don't have the license to purchase the refrigerant. -- Neither do I, which is a real pain given the tight controls on the selling of Freon these days.)

Good Luck, DoN.

[Tony]

This is symptomatic of a bad compressor. Try testing the motor leads for a dead short (to each other and ground). There are start and run leads. You may need a HVAC guy to replace your compressor and recharge the system.

Tony

[Ignoramus2645]

Um, no, that could not be the case. If I disconnect the cap's fat blue lead and let the cap hang in the air, the breaker does not blow, the blower runs, and the compressor hums (I am sure that it does not run).

It is very likely the cap.

i

[Richard J Kinch]

Two capacitors, in one can, with a common terminal.

[Noon-Air]

Ok, lets say that you *DO* figure out what the problem is... do you have the correct parts on your truck to actually make the repair?

[DoN. Nichols]

And -- you can see the time delay module under the varnish (or whatever) at the bottom right of the diagram -- in series with the contactor coil, and an optional switch in which the high pressure side of the refrigerant pump can prevent start even if the timer has timed out. (But -- that is described as "optional", and the delay timer (as much as I can make out under the varnish) is not described as "optional", but it *is* described as "accessory" -- so I suspect that you have two failures -- the compressor, and the delay timer which induced the compressor failure, and which will induce it again if not replaced when the compressor is replaced.

It looks as though there is only one set of contacts in the contactor, and the other set of terminals serves simply as a terminal strip to carry the other side of the 240 VAC over without switching it.

This is *not* a good time of the year to have an air conditioner fail -- and also not a good time to try to get a licensed professional out to work on it.

You might save one round trip (probably with significant delays) if you warn them ahead of time that the compressor is likely dead. If you can, dig up the numbers from the compressor case -- or if you can't get to that, at least the model number of the overall device.

Good Luck, DoN.

[Richard J Kinch]

Values should be on the old capacitor.

Common terminal. The can is (unless defective) isolated.

One of your terminals may be shorted to the (grounded) can, thus causing your circuit breaker overload.

Costs about $10 or $20 at

to get a replacement. Also all over eBay.

[mm]

I am an amateur, but...

At this stage I don't think you should be trying to measure amps, and since it is wet, I don't think you should be trying to measure volts.

You should turn off the breaker so that all hot leads to the compressor are disconnected, and when you verify that there is no voltage, you can start measuring ohmage, resistance btween the hot and hot, or the hot and the ground, in your compressor.

First realize that there are two power supplies to the compressor, a

110 volt circuit that uses the thermostat and the control board to control the contactor, probably the thing you heard humming below, and a 220 volt circuit that actually powers the compressor.

BOTH CBs should be off.

Everything below assumes that the problem is in the 220 volt circuit. If that's not true, post back.

If you got 200 amps, and even if you got less, but it kept tripping the breaker, it's pretty clear (though I supppose it's not entirely certain) that you have a short. An ohmmeter is the way to find it.

The capacitor could be the place, and that would be good I guess because they are cheap comparitively. IIUC, new caps have two caps in one can. One could be shorted while the other is fine. You shouldn't measure for a short until you meausure voltage between the common and each of the other leads. If the cap is bad, one might have voltage and the other might not. The voltage might be enough to burn out part of your ohmmeter. If the cap is still good, both halves might be hot. If the cap is hot, holding a charge, and has stayed hot while it was raining, it's probably good. But if you want to check more, if it does have voltage, you could apply a screwdriver with an insulated handle to the two connectors and watch for a spark. Then do it again and watch for a second spark. That should discharge the cap. Then you can measure the ohms and they should be verrrry low as current flows from your meter into the cap. With a small cap, the ohms would start to increase as the cap filled, but I reallly don't know how long that would take with one of these. This is much easier to see with an analog meter, a meter with a needle. The needle goes all the way to the right, and slowly back to the left. But like I saw with these caps with high capacitance (and 25 microf is a lot) I don't know how long this takes. I'd say if at the start each part of the cap shows substantail voltage, the cap is good.

It's not likely the contactor is shorted, and if it is, you should see sparking damage. If you want to check one more time, you can be looking at it when the 220 breaker is turned on one more time, and you can watch the contactor. If it trips but you don't see sparks there, that's not the problem.

I don't know if the outside fan is 110 or 220. I guess if it doesn't turn when the inside fan is turning, it's 220. That motor is a lot cheaper than a compressor. With my ac, you can take off the case, take off the fan blade, take off the plate, I guess it is a rain shield, and look for spark damage, and have someone look at that at the smae time yuou turn on the breaker, and see if that sparks, although maybe it sparks underneath where you can't see it.

Oh yeah, you should also measure the resistance of the two wires to the fan, and the two wires to the compressor. The compressor uses a lot of current so the resistance might be low normally. (I think it would present as higher to the AC house current than it does to the DC current from the battery in your ohmmeter.) I don't know what would be correct. Zero is too low.

This was worth doing. Is this the same CB that keeps tripping and where you measured 200 amps. I don't think so, but you didn't draw a distinction.

Oh, don't complain about Oscar's jokes. It was funny and beggars can't be choosers. :)

[mm]

If there is a short in the cap, that's one place there won't be any visible sparking and maybe nothing visible.

It says what it is on the can. If not, I guess a diagram, and if not, maybe the AC supply house knows. If you know the value you want you might get it cheaper at an electronics supply house, but they might not even sell one that big. Never tried.

Probably.

I doubt it.

If it's the cap, you may have gotten off cheap. Good for you.

[Richard J Kinch]

AC electrolytic capacitors of this type are not sold by electronics distribution.

[Ignoramus2645]

Yes, that's right. You got it 100%. Here's the schematic:

i

[Ignoramus2645]

It depends. If it is a cap, I can buy one tomorrow. If it is the motor shorted, I will have to hire a pro.

i

[Ignoramus2645]

The control voltage is 24VAC.

OK, thanks. I appreciate your tips, will try some of them for sure.

i

[Ignoramus2645]

Makes sense.

Does not seem to be the case for me (the contactor is energized).

That could be. I did a few more measurements. I will post a summary soon.

That's correct, I saw a diagram (and posted it).

Sure.

I am afraid that it is the case, as well (see my UPDATE #2 that I am about to post).

i

[Ignoramus2645]

I am now convinced that it is true, the compressor unit is dead. These guys that service my equipment are in my town, a trip should not be too much for them, and also, after looking at the outside unit, I think that I want something better.

i

[mm]

Yeah I know, but I still think of it as 110 because that's what it is before it goes throught the transformer.

[stevek]