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  1. #1

    Momentary Service Interuption Causes Compressor to be Loud/Vibrate on Restart

    Hello to everyone,

    About a year ago I had my compressor and air handler replaced [appropriately sized and matched] by a licensed installer. I also had a complete new 200 amp service installed as well as whole-house surge protection. This work was also done by a licensed electrician and I am confident that all of this was quality work [overly so?].

    Recently however I have noticed that when a storm interrupts service to the neighborhood/house [usually lasting about half-a-second] if the A/C was on at the time of the interruption it will come back on immediately but the noise from the compressor [Goodman GSX 4-ton w/Copeland Scroll] will be a good three or four times the normal level and there is a terrible vibration.

    Every time I have checked after each incident I can see that the main panel breaker has not tripped. The only remedy seems to be to turn the system off at the thermostat and wait for at least 5 minutes before restarting - then the compressor comes back on and sounds and acts normal [FYI - always cool air and no icing].

    Per the forums rules I am not asking for a step-by-step DIY if this is something major but is this normal behavior? Is there something [hopefully simple and cheap] that can be done to rectify this problem [if it is indeed a "problem"]?

    Thank you in advance.

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    You need a thermostat with a built in five minute time delay upon power loss and restoration.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #3
    Quote Originally Posted by shophound View Post
    You need a thermostat with a built in five minute time delay upon power loss and restoration.
    That simple - really? That would be great!

    Thank you.

    Do you mind if I ask what specifically is going on, is this a common or universal issue? I don't question your solution but I am curious as to the mechanics of what is happening here, if only to satisfy my own curiosity.

    Thanks again.

  4. #4
    Join Date
    May 2011
    Location
    Ripley, WV
    Posts
    1,326
    When the power is interrupted and stops the compressor momentarily and instantly restarts it. When it does that it doesn't give enough time for the system pressures to equalize, which means it tries to start against a high head pressure. This causes your loud noise and vibrating, and even worse it can be hard on a compressor to start like that. Shophound is correct on the thermostat with a built in delay, just make sure its a quality one.

  5. #5
    Quote Originally Posted by Rob_in_WV View Post
    When the power is interrupted and stops the compressor momentarily and instantly restarts it. When it does that it doesn't give enough time for the system pressures to equalize, which means it tries to start against a high head pressure. This causes your loud noise and vibrating, and even worse it can be hard on a compressor to start like that. Shophound is correct on the thermostat with a built in delay, just make sure its a quality one.
    Thank you both.

    I can see that my Hunter 4486 does not have this feature. Do either of you have any recommendations for a quality replacement with similar features and price [if such a thing exists]?

  6. #6
    Join Date
    Jun 2010
    Location
    S. Texas
    Posts
    63
    The comp is restarting against a load, maximum discharge pressure. When the unit shuts down the pressures equalize; drop a lot. Easier to start. Oh, and a scroll might be restarting in reverse with a brief interruption of power; makes serious noise I'm told. Doesn't compress too well in reverse either, thats why you have to shut it off again yourself and wait 5 min.

  7. #7
    Join Date
    Jun 2011
    Location
    sunnny south west florida
    Posts
    34
    make sure the stat will give you time delay function in a power outage. many of the thermostats that have a built in 5 minuet time delay can be wired in such a way that batteries are used to supply power for the stat. so when the power goes out the time delay doesn't kick in because the stat never lost power. perhaps a safer bet would be to have a 5 minuet delay on break wired at the condenser out side. those little time delays are probably cheaper than a new stat as well, and easier to install. If you have some one install a new t stat for you , make sure you simulate power failure by tossing the breakers,on and off, before you let him leave.

  8. #8
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,590
    Good point icool, some of the new ones don't catch the power outage, they kick to battery.

    I think what's happening is the scroll starts up backwards and they don't like that! If these glitches are common in your area, a dealer can put a time delay in the outdoor unit. In the good old days, they were standard from the factory. The earlier scrolls were even worse at starting backwards like this, supposedly the newer ones don't do it but I hear many spin backwards on stop so they sure can.

  9. #9
    Join Date
    Mar 2009
    Location
    Hollywood, Florida
    Posts
    310
    Here in South Florida we have constant power interruptions. Have your HVAC guy install a time delay at the condenser. They get wired in-line on the low voltage line. Works great even with cheap thermostats.


  10. #10
    Join Date
    Jun 2011
    Location
    sunnny south west florida
    Posts
    34
    hunters are no good, stick with Honeywell. we use. Honeywell pro 3000, non programmable
    pro 4000 programmable , and the one i own at home is the Honeywell vision pro 8000, with humidity function. make sure it steals power from the air handler with no batteries installed. i have noticed that when the common wire is used with the batteries installed it can some times blow the the low voltage fuse for the transformer when switched from cool to heat.

  11. #11
    Quote Originally Posted by BaldLoonie View Post
    Good point icool, some of the new ones don't catch the power outage, they kick to battery.

    I think what's happening is the scroll starts up backwards and they don't like that! If these glitches are common in your area, a dealer can put a time delay in the outdoor unit. In the good old days, they were standard from the factory. The earlier scrolls were even worse at starting backwards like this, supposedly the newer ones don't do it but I hear many spin backwards on stop so they sure can.
    This sounds like what is happening.

    If I turn the system off at the thermostat [regardless of environmental conditions] it won't let me turn it back on [for a minimum of 3.5 minutes according to the manual] but the manual also states clearly that the delay function will not operate when there is a loss of power.

    Also yes, we do have frequent power interruptions due to t-storms so having a delay circuit installed at the compressor sounds like the best option.

    Regional variations aside, how much should such a job run, if I might ask?

    And again, my thanks to everyone.

  12. #12
    Join Date
    Jun 2011
    Location
    sunnny south west florida
    Posts
    34
    i am new so i don't know if they allow pricing but it should be cheaper than a new stat, and maybe if you have a regular service done on the system while they do it they can deduct there travel expense. That's what we do any way. its a cheap part and takes seconds to install, use some one you trust.

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