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  1. #1
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    Jun 2019
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    Confused Mini split coolig more when it is hot

    Hello

    I've a potential issue with a recently installed mini split: when it is hot outside (90-95F), it keeps perfectly the set indoor temperature (e.g. 76F set, 76F measured indoor after it has been working for a while).

    However late afternoon and night, when outside temperatures go down (85-90F), the indoor temperature goes up... e.g. 76F set by RC but getting 79-80F inside... AC is on all the time.

    Why would it not keep inside temperature to the set limit, when it is getting colder outside? Should I be worried about a technical issue here?

  2. #2
    Join Date
    Oct 2011
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    Gladstone, Oregon (Portland)
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    Quote Originally Posted by gustavhorna View Post
    Hello

    I've a potential issue with a recently installed mini split: when it is hot outside (90-95F), it keeps perfectly the set indoor temperature (e.g. 76F set, 76F measured indoor after it has been working for a while).

    However late afternoon and night, when outside temperatures go down (85-90F), the indoor temperature goes up... e.g. 76F set by RC but getting 79-80F inside... AC is on all the time.

    Why would it not keep inside temperature to the set limit, when it is getting colder outside? Should I be worried about a technical issue here?
    Coincidence. Call a tech.

  3. #3
    Join Date
    Aug 2002
    Location
    Southold, NY
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    Without real facts my 1st guess is the units oversized and runs continuously during the heat of the day. At night it shuts down with minimum off times!

  4. #4
    Join Date
    Jan 2008
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    New Jersey
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    Does this mini split use a return sensor at the unit or room t-stat for sensing? Do you have a make and model?

    Sent from my ASUS_P00J using Tapatalk

  5. #5
    Join Date
    Jun 2019
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    Thread Starter
    innovair 9000 btu

    yes it has a sensor on the indoor unit. I wonder why it is able to cool during the hot time of the day but not during colder night time - does not make sense. The sensor should signal all day around what the inside temp is.

    I could understand the inverse problem of undersized unit not cooling enough during the hot time... but not cooling during cold time? It keeps the indoor temp correctly from about 11am to 6pm, but then it starts to rise while it is getting colder outside. I was supposing that maybe it is getting too much sunshine on the outdoor unit so it works harder than it should, however then I've built a small roof over the outside unit (about 1.5 feet over it) to shield the sunshine off but it has no measurable influence on the indoor temp. weird.

  6. #6
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    Jun 2019
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    Thread Starter
    ps do not think it is oversized, the room is small (around 300 sqft) but it has a high ceiling and 9000 is the smallest regular size on the market (unless you want to take into account some super expensive 6000 Mitsubishi). The inverter can modulate from 3000 to 10.000 btu according to the type plate

  7. #7
    Join Date
    Jan 2008
    Location
    New Jersey
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    Where are you reading the indoor temp from? Is it possible return temp is at setpoint , but t-stat is readings higher temp. If you are getting your temp readings from the stat.

    Sent from my ASUS_P00J using Tapatalk

  8. #8
    Join Date
    Jun 2019
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    Thread Starter
    reading it with digital thermometer in the middle of the room.

    The room also feels colder during hot time, it is noticeably colder.

    The point is, if I read 76F when 76F is set during the hot time, why it can't cool it to the same 76F while it is easier for the unit during night time? Something does not sum up here

  9. #9
    Join Date
    Aug 2002
    Location
    Southold, NY
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    Quote Originally Posted by gustavhorna View Post
    ps do not think it is oversized, the room is small (around 300 sqft) but it has a high ceiling and 9000 is the smallest regular size on the market (unless you want to take into account some super expensive 6000 Mitsubishi). The inverter can modulate from 3000 to 10.000 btu according to the type plate
    Super expensive!

    You get what you pay for.

    3/4-Ton for 300 Sq Ft
    YES it’s oversized!!!

  10. #10
    Join Date
    Aug 2002
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    Southold, NY
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    Quote Originally Posted by pecmsg View Post
    Super expensive!

    You get what you pay for.

    3/4-Ton for 300 Sq Ft
    YES it’s oversized!!!
    I’ll prove it.
    Bet you a 3000BTU window shaker controls temp and humidity better!

  11. #11
    Join Date
    Jun 2019
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    the room has an about 12ft ceiling. you cannot stick only to the 2 dimensional size, the air content in the room is the relevant parameter.

    Moreover the unit works at about 80% of the capacity at early afternoon (looking by amps and spec), so I'm quite sure it is not oversized. You still need some reserve, it might get even hotter or someone might want to have not 76F but lets say 70F... see my point?

  12. #12
    Join Date
    Jun 2019
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    Thread Starter
    Window AC is a no go in that house and a smaller split? Where to get one at a reasonable price?

  13. #13
    Join Date
    Aug 2002
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    Quote Originally Posted by gustavhorna View Post
    the room has an about 12ft ceiling. you cannot stick only to the 2 dimensional size, the air content in the room is the relevant parameter.

    Moreover the unit works at about 80% of the capacity at early afternoon (looking by amps and spec), so I'm quite sure it is not oversized. You still need some reserve, it might get even hotter or someone might want to have not 76F but lets say 70F... see my point?
    Believe what you want!

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