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Posted by Ignoramus2645 on August 3, 2006, 12:35 am
>> Some new developments.
>>
>> 1. The main 24VAC coil contactor is fine, I must have mis-measured
>> something.
>>
>> 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
>> shot.
>
> 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.)
Makes sense.
> 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.
Does not seem to be the case for me (the contactor is energized).
> 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.
That could be. I did a few more measurements. I will post a summary
soon.
> 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.
>
>> 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?
>
> I don't think that they would have anything connected to the can
> at these voltages, so there should be a common terminal.
That's correct, I saw a diagram (and posted it).
> Do you have a capacitance meter to try on the capacitor?
Sure.
>> Answers will be appreciated.
>
> 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.)
I am afraid that it is the case, as well (see my UPDATE #2 that I am
about to post).
i
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