It is quite obviously not very relevant, but there is very solid 24
VAC as input to the contactor's coil.
One pair of contacts (across the contactor) measures 0 ohm. Another
pair, strangely, measures infinity, which is quite strange as the
contactor ought to be closed for a power fault like this to occur
(barring some very strange troubles). I left the outside unit due to
the rain that resumed, will come back there soon.
I am not used to seeing such strange contactors, all contactors that I
dealt with, to date, were three pole contactors for 3 phase motors.
Also, can someone explain me why the capacitor has three sets of
terminals. What is the purpose of the third terminal. Thanks.
On Thu, 03 Aug 2006 02:37:39 GMT, Ignoramus2645
I think that I was wrong. The contactor is OK. I must have mismeasured
something. It has zero ohms across bost pairs of contacts.
I am going to post a little update, it is a little more apparent to
me -- see my separate post.
Some new developments.
1. The main 24VAC coil contactor is fine, I must have mis-measured
2. I understand why there are three terminals on the capacitor. There
are really two capacitors in one "can". They share a common. One
capacitor is for fan and another is for the main compressor motor.
3. If I disconnect one lead to the capacitor (a fat blue lead), then,
if my wife resets the breaker, the cooling fan starts up just fine and
I hear humming noise from the motor. I did not let that continue for
much more than 2 seconds.
My conclusion is that most likely, the capacitor for the main motor is
Q U E S T I O N S:
1. Anyone know how to calculate required capacitance by "rated amps"
of the motor? (I realize that motors are all different, but I need
some way to guesstimate)
2. Do the two coexisting caps share a common terminal, or does one of
them have one contact on top and another being the (grounded) can?
Answers will be appreciated.
More to follow.
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.
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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.
Notice in series with the "C" terminal on the Compressor, there is an
overload device. This is a self reseting current limit that most likely
is part of the plug that connects to the C, S, and R terminals of the
compressor (these stand for Common, Start and Run). Or it is a separate
device but in thermal contact with the compressor can. Klicks-on is a
Texas Instumentcompany that makes these. The diagram indicates "if
used" but I believe it has to be there to protect the compressor motor
in the case where it has a locked rotor from differential pressure, and
it does not have enough starting torque.
Pull the C,S, and R plug, and perform a resistance measurement between
C and S and C and R. These should be less then 10 ohm measurements.
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