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  1. #1
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    Unbelievable Coincidence with 3 A/C units at the same time

    I live in Georgia and it was 95 degrees yesterday. I have 4 individual systems in my home that were all installed last year. Single stage gas furnaces inside with 5 speed ecm blowers and the outdoor units are all single stage a/c units. One 3 ton for the upstairs, a 3 ton and a 2.5 ton for the main floor and a 3 ton for the full basement. Anyway, yesterday at about 7:30 PM I noticed the air in the home was getting a little stuffy and warm even though the units were still running and the thermostat still indicated the a/c was on and calling for a/c. Then I go upstairs and that unit is doing the same thing. Then, unbelievably, my other main floor unit is blowing warm also. I have 3 out of 4 units that are all-of-a-sudden not producing cold air and all at the exact same time. I go outside and, yes, all 3 outdoor units are running with the fan on top but I can tell the compressors are NOT running. The air coming out of the top of the condensers is cool instead of warm and the big copper line going into the compressor is still wet but it is much warmer than normal.

    I turn them all off at the thermostat and turn them back on a couple minutes later and the outdoor units click but no compressor kicks on and then about 2 seconds later the fan on the top of the condesor starts spinning like normal. Did this a couple more times with the same result. Let them sit for 45 minutes and they all kicked back on and work fine. These units have worked perfectly all summer and never have done this before that I know of. I suppose there is some kind of safety switch that was preventing the compressor from staying on and it just needed to rest for a few minutes before it restarted???

    The 4th unit is for the basement and I turned it on and it started working correctly right away but since it is the basement unit it had only ran 2 hours earlier in the day.

    So, what do you guys think of this??? Is it normal for a compressor to shut down for a few minutes to cool off? What are the odds that 3 individual units did the exact same thing at the exact same time of day? It is starting to cool off in the evenings here now but it is still definitely A/C weather here in Georgia even up till Midnight.
    Thanks,
    BB

  2. #2
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    Nov 2006
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    Could there have been a low voltage issue which affected all the units?

    11.5 tons is a whale of a lot of cooling. How big is your house that it needs that much air conditioning?
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  3. #3
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    There is 8600 square feet heated and cooled but more importantly, lots of windows and 20 foot ceilings. All 4 systems operate at .5 static pressure or less. I thought originally that I blew the run capacitors from some kind of power surge.

  4. #4
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    Quote Originally Posted by bluebelly View Post
    There is 8600 square feet heated and cooled but more importantly, lots of windows and 20 foot ceilings. All 4 systems operate at .5 static pressure or less. I thought originally that I blew the run capacitors from some kind of power surge.
    That is big. Do the systems maintain a low humidity in the house?
    AOP Rules: Rules For Equipment Owners.

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    There = not here. Their = possessive pronoun. They're = they are
    It's = contraction of it is. Its = the possessive form of it
    Too = also. To = expressing motion. Two = 2
    Then = after that, next. Than = indicates a comparison.
    Questions should end with a question mark "?" Statements end with a period "."

  5. #5
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    Yes, they keep the humidity at about 44% to 47% during the most hot and humid time of the year. I am taking that reading off of the thermostat and I have a couple of other hygrometers placed around the house to monitor the humidity. All of them read within 1% of each-other so I believe them to be accurate. I save the condensation from the top floor 3 ton unit and it produces 8 to 10 gallons of water per 24 hour period. It seems everything is ballanced well.

  6. #6
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    Unbelievable Coincidence with 3 A/C units at the same time

    Do you have 1ph or 3ph systems? If 3ph it could have dropped the high leg at the pole.


    Sent from my iPhone using Tapatalk
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards" ~ Vernon Law

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  7. #7
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    These units are all single phase.

    Do you think a drop or surge in voltage could cause a compressor to stop running but the fan on top of the condenser keeps running? I just can't get over how 3 units exhibited the same problem at the same time. I find it hard to believe that at the same time all 3 compressors tripped a safety switch due to heat or pressure. I think it has to be an electrical cause.

  8. #8
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    With that much equipment consider getting Phase monitors

  9. #9
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    Quote Originally Posted by bluebelly View Post
    Do you think a drop or surge in voltage could cause a compressor to stop running but the fan on top of the condenser keeps running? .
    Could have caused the compressors to short cycle and not come back on, and yes the fans would still run.


    Sent from my iPhone using Tapatalk
    __________________________________________________ _______________________
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    "It's what you learn after you know it all that counts." ~ John Wooden



  10. #10
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    Low line voltage makes the compressor and motor over heat,both have internal thermal protection. Fan motors cool off in a few minutes while compressors can take hours to cool.

  11. Likes Mr Bill liked this post
  12. #11
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    Mr. Bill,

    You wrote : "Could have caused the compressors to short cycle and not come back on, and yes the fans would still run."


    By "short cycle" do you mean the a/c shut down and then tried to re-start right away, maybe a few seconds later? And this would cause the compressors to not re-start? If so, this sounds familiar. I remember messing with the thermostat earlier this year and I accidently turned the a/c back on after it just went off. I seem to remember the a/c not blowing cold air for a few minutes.

  13. #12
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    Quote Originally Posted by bluebelly View Post
    Mr. Bill, By "short cycle" do you mean the a/c shut down and then tried to re-start right away, maybe a few seconds later? And this would cause the compressors to not re-start?
    Correct.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards" ~ Vernon Law

    "Skilled Labor Isn't Cheap, Cheap Labor Isn't Skilled" ~ Unknown

    "When the teachers become unteachable we're all in trouble"

    "It's what you learn after you know it all that counts." ~ John Wooden



  14. #13
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    Thread Starter
    If two of my units started at exactly the same time would that have caused a voltage drop significant enough to cause this? I have a boat with 3 different a/c systems and they have a black box wired between them that would ensure a 15 second difference between start ups and shut downs so as not to overload the shore power to the boat or the onboard generator when underway.

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