Should my house reach 75 degrees?

Hi folks, I have a question that may be tough to answer. I have a 1200 square foot, single story home. My HVAC unit is a heat pump/AC unit. I'm not sure about the condensor size, but it uses 5lbs of freon...
for the past week, it's been about 99 degrees outside and we've had the AC set to 75 - but it never reaches that temp. it only gets to 78.5 and the unit just keeps running. Shouldn't it be able to get to 75 without a problem? We have insulation in the attic, and the thermostat is not in direct sunlight. All together, the home has 9 registers/vents. 2 of which are in the room with the thermostat. The air coming out feels cool, but I don't like having it on constantly (due to cost). So I've resolved myself to setting the thermo to 78... and letting it shut off on its own.
is this normal (due to it just being so hot outside perhaps?) I live in southeast virginia where it's very humid.
thanks everyone, - J
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Sounds like the system is at its design capacity and is operating normally.

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First, we have no idea whether your unit is sized to maintain 75 degrees. It may or may not be undersized.
Second, we have no idea whether your unit is operating properly without any operational data.
Third, when was the last time you had your unit serviced?
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last week, I had a technician come out and fill it with freon. he did a local check for leaks, and he checked the unit in the attic - but did not do a pressure test. It required the full 5lbs of freon... the house was dormant for a number of years before we bought it.... so we figured it just leaked out the valve on the condenser. i'm not sure I have any other data that would be of use. I'm guessing it is probably just undersized...
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last week, I had a technician come out and fill it with freon. he did a local check for leaks, and he checked the unit in the attic - but did not do a pressure test. It required the full 5lbs of freon... the house was dormant for a number of years before we bought it.... so we figured it just leaked out the valve on the condenser. i'm not sure I have any other data that would be of use. I'm guessing it is probably just undersized...
Probably *NOT* undersized... check the system design parameters for your area... My money is on the system being correctly sized, or real close to it. Gazing into my crystal ball, I would venture to say that system design in your area is probably real close to 95/95 outside and *maintain* 75/50 inside, withthe system running constantly....and as it gets warmer outside and exceeds the design parameters, the IDT will increase accordingly. Best bet is to set your comfort level on the thermostat, and leave it alone...let it do its job of controlling the system. If it runs continuously during the heat of the day, then so be it. Just remember that as long as the system is running, its pulling moisture and humidity out of the air so you can remain comfortable at a higher temperature.
Thus ends the lesson
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degrees.
continuously
the
Steve its a obvious trool given he added 5lbs then gonna be ~3-1/2 ton min empty and w/ 1200 sf of area you arent hardly even gonna need to have walls on the structure.
--


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Sorry, but lbs of refrigerant doesn't translate to tonnage. I just worked on a 2 1/2 ton unit where the factory charge of R-22 was 6 lbs.
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Quantity of R-22 isn't an issue, I have done some work on systems where a 3 ton heat pump system took close to 18 pounds, a 4 ton took 22 pounds...otoh, if you only talking about a builders grade, 10SEER straight A/C, and it was dead empty, I would almost be inclined to agree....but we don't know what the OP has.
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unit.
to
The
78...
live
without
quoted
your
to
75/50
as
min
3
pounds...otoh,
was
Definately he has a trolling license then......
--




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Here is a way to determine if that is the problem or not. Starting with a warm house (82 or 83) turn on the AC and make a record of how the temperature falls as a function of time. If the A/C unit is undersized, then the temperature will start falling and then gradually level off at 78.5 or something. If you draw a graph of the temperature, it will look like an inverse exponential. However, if you see essentially a straight-line temperature fall that abruptly hits 78.5 and stays there, then that points to a control problem.
Another test would be to observe the behavior on a day that is not so hot (or at night). If the temperature still levels off at 78.5, that is a control problem. Because if the A/C is undersized, then it will still be able to achieve a lower temperature when the outside temperatures is lower.
Robert Scott Ypsilanti, Michigan
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