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Old 03-12-2014, 01:45 PM   #16
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Do I really need a new compresser?


When the pressures equalize in the off cycle the compressor starts in an unloaded condition. As the compressor starts to turn it will draw high starting current through the start winding (typically approx. 5-6 times the running current), this happens for usually less than 1-2 seconds. Once the compressor starts to turn and is up to speed the start winding is either de-energized or allowed to continue to be in the circuit at a much lower amperage.
By energizing the compressor before the pressures had a chance to equalize you tried to start it in a loaded condition and the start winding would have drawn the high amperage for a longer period of time. That makes the winding get very hot and it is possible that one of the winding wires overheated and burnt off. If that burnt winding came in contact with the shell housing of the unit it could have shorted to the unit housing. Most times that will follow the bonding conductor back to the panel and blow the breaker.( which is what is supposed to happen)

Sometimes the bonding conductor is not complete from the unit to the house ( maybe it is not connected in the unit, or the disconnect, or at the panel) that is when you can have some big troubles as your circuit protection circuit is not complete. Another option would be that that winding could short to an additional winding inside the compressor and not come in contact with the bonded housing.

Your power can still flow in a restricted fashion to ground through the windings of the compressor motor, and can affect the condenser fan as they are tied to common terminals on the contactor and have some relationship through the capacitor if it is shared and or shorted.

It gets long winded and complicated from there, but that is the readers digest version as I see it.

There is an internal overload in the compressor that is there to protect it from overheating, and if the compressor does overheat it usually resets itself, but that doesn't always happen. It is also in series with the common of the compressor, so all running current passes through it, so if you have high currents for prolonged periods it can burn its contacts, or make it not close again in the future. If the compressor is humming, I would assume this has reset and you have either a burnt start winding or a bad compressor ( seized).
(Providing that it is in fact getting proper voltage)

Hopefully that helps a bit

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Old 03-12-2014, 01:49 PM   #17
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Do I really need a new compresser?


EXACTLY my words and you saved me the headache. At 10 yrs old the compressor may be worn and ready to die and I hate to say it but some builders grade units like brand G did not always spec out the Cadillac compressor if you get my meaning. Other brands did the same. The wirng scenario is complicated and you need to be a tech and understand PSC permanent split capacitor motors and the circuitry to understand how the fan motor can get backfed or low voltage or turn backwards.
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Old 03-12-2014, 01:50 PM   #18
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Do I really need a new compresser?


Quote:
Originally Posted by HVACDave View Post
When the pressures equalize in the off cycle the compressor starts in an unloaded condition. As the compressor starts to turn it will draw high starting current through the start winding (typically approx. 5-6 times the running current), this happens for usually less than 1-2 seconds. Once the compressor starts to turn and is up to speed the start winding is either de-energized or allowed to continue to be in the circuit at a much lower amperage.
By energizing the compressor before the pressures had a chance to equalize you tried to start it in a loaded condition and the start winding would have drawn the high amperage for a longer period of time. That makes the winding get very hot and it is possible that one of the winding wires overheated and burnt off. If that burnt winding came in contact with the shell housing of the unit it could have shorted to the unit housing. Most times that will follow the bonding conductor back to the panel and blow the breaker.( which is what is supposed to happen)

Sometimes the bonding conductor is not complete from the unit to the house ( maybe it is not connected in the unit, or the disconnect, or at the panel) that is when you can have some big troubles as your circuit protection circuit is not complete. Another option would be that that winding could short to an additional winding inside the compressor and not come in contact with the bonded housing.

Your power can still flow in a restricted fashion to ground through the windings of the compressor motor, and can affect the condenser fan as they are tied to common terminals on the contactor and have some relationship through the capacitor if it is shared and or shorted.

It gets long winded and complicated from there, but that is the readers digest version as I see it.

There is an internal overload in the compressor that is there to protect it from overheating, and if the compressor does overheat it usually resets itself, but that doesn't always happen. It is also in series with the common of the compressor, so all running current passes through it, so if you have high currents for prolonged periods it can burn its contacts, or make it not close again in the future. If the compressor is humming, I would assume this has reset and you have either a burnt start winding or a bad compressor ( seized).
(Providing that it is in fact getting proper voltage)

Hopefully that helps a bit
Wow! Thanks for that! I know you certainly helped myself and probably a few hundred more that come across this thread via internet search!
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Old 03-12-2014, 01:53 PM   #19
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Do I really need a new compresser?


Yur lucky you caught me and Dave. I would guess that only 10% of the techs out there truly understand this scenario/issue.

Pay it Forward and help someone else.
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Old 03-12-2014, 01:57 PM   #20
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Do I really need a new compresser?


Thanks for the compliments, I am rarely on here, but enjoy the conversations that I do get to participate in. This site has some very good techs that frequent it and I know that many get good solid info here.
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Old 03-12-2014, 03:38 PM   #21
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Do I really need a new compresser?


Has any one taken the time and trouble to check the disconnect & see if it has not been compromised ?

If it is defective , it could easily result in bad power quality .

Easy and inexpensive to replace , to .

Object lesson for today , do not mess with the disconnect with the init running , unless it is an emergency situation . Then do not turn the disconnect back on until all problems are taken care of . Turn the thermostat off before you turn the disconnect back on .

Wake up . Electricity can be dangerous , especially if you do not know what you are doing . And it may hace cost the OP the price of replacing the HVAC unit .

Even worse if the disconnect had blown up on him . If you do not know what you are doing , stand back and keep your hands in your pockets .

God bless
Wyr

Last edited by WyrTwister; 03-12-2014 at 03:45 PM.
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Old 03-12-2014, 03:39 PM   #22
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Do I really need a new compresser?


Quote:
Originally Posted by WyrTwister View Post
Has any one taken the time and trouble to check the disconnect & see if it has not been compromised ?

If it is defective , it could easily result in bad power quality .

Easy and inexpensive ro replace , to .

God bless
Wyr

Yes we did. We even hard wired it together bypassing the disconnect plug.
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Old 03-12-2014, 05:06 PM   #23
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Do I really need a new compresser?


For the cost of a hard start kit. I would try one before just replacing the compressor or entire A/C. I would probably also change out the run capacitor. I've had more then one show it was good when I used a tester on it. But the compressor wouldn't run. replaced the capacitor and it ran.

Your call though.
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Old 03-12-2014, 07:46 PM   #24
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Do I really need a new compresser?


did anyone put a meter on the thing and see if its still delivering 240Volts
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Old 03-12-2014, 07:46 PM   #25
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Do I really need a new compresser?


disconnect I mean
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Old 03-13-2014, 04:20 PM   #26
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Do I really need a new compresser?


Let's go back to square 1 for a regroup. Why was the disconnect pulled while it was running in the 1st place ? Who pulled it? Was there a problem to start with ? Is that why it was pulled? How bout some history? Something missing here.
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Old Yesterday, 08:23 AM   #27
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Do I really need a new compresser?


has anyone check the run cap you said the fan running slow sounds like your cap maybe the problem and check the ohms across the run to common and start to common on compressor
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Old Yesterday, 12:24 PM   #28
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^^^^^^^

I was about to ask the same thing, maybe the run cap blew?
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Old Yesterday, 11:55 PM   #29
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Do I really need a new compresser?


need a meter to check for 240 volts at contactor and or at breaker. Reset breaker.

compressor is not harmed whatsoever, electrical feed such as a breaker (usually a double pole which could result in one leg soft arced) or possibly a wire melted.

Pulling out a disconnect and re-inserting it quickly only short cycles electrical path, does no damage to compressor.

Certainly it may not start immediately, but leave disconnect in and it should start next few rounds if all else is well such as 240 volts present, cap good and all wires good.

Count me in the top 1% of realists.

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