On Thu, 03 Aug 2006 00:16:29 -0400, mm wrote:
On Thu, 03 Aug 2006 02:58:24 GMT, Ignoramus2645
wrote:

On Thu, 03 Aug 2006 02:48:24 GMT, Oscar_Lives wrote:

"Ignoramus2645" wrote in message
. ..
I have a central A/C. Around when there was a thunderstorm,
electricity flickered about 2-3 times in our house.

Now our A/C is not working. The inside is all fine, the fan runs etc.

I am doing investigation and will post in this thread, but the breaker
popped and any attempt to reset it pops it again. I tried to measure
amps with my ammeter, it was quite hard to do due to breaker popping
soon, but the highest measure I got was about 200 amps.

I am going to open up the case now to have a quick look, I will be
running back and forth. My hope is that it is something simple like
capacitor shorted, but it easily could be worse (eg motor shorted).

i


Have your buddy hold the breaker handle over for a while so the current can
stabilize and you can get a better reading.

I tried it, and I think that the breaker is good enough to reset
despite that. In any case, it is kind of pointless, as I know that the
current is too large and lasts too long.

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.

The control voltage is 24VAC.

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.

I tried asking my wife to turn on the CB while I was outside, I heard
some humming noise and then stop.

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.

I will wait a little until rain
subsides and will go back.

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


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

i