Correct sizing of a/c?

With the outside air at 90 and a RH of 50%, the inside temp at 80, with a differential of 1.5 degrees, my A/C is on for 30 minutes and off for 40 minutes.
Is this 3t A/C sized correctly? I would like to know because the A/C is getting old and I want to replace it with a new one. If this one is sized correctly I will know what size to look for .
Thank you
--
Walter
www.rationality.net
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Looks to me to be a bit over sized. A Manual J is the only accurate way to know for sure, anything else is a guess! My AC runs constantly at 95 degrees and it will maintain a indoor temp of 74. Sized right on in my book! Greg
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This is Turtle.
I can keep 70F indoors with it 107F outdoors. Now it will run about 100% of the time during the day lite hours. The Manual J said 3.25 tons and I upped to 3.5 tons. That 1/4 ton would make the difference at 107F outdoors these days. Also that 1/4 ton hurts me on a 85F outdoor temp with not enough of run time. i then installed a humidistat to override and keep a 55% RH or below.
TURTLE
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Turtle,
1/4 ton oversized should not hurt. In the old days we figured up to 25% oversized was OK. Now it is recommended to oversize no more than 15%. Of course, you are sometimes limited by available sizes.
Walter,
If the conditions stated by you are design conditions for your area, you are WAY oversized! When you are at design conditions, inside and outside, your unit should run constantle or nearly constantly.
Stretch
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Walter R. posted for all of us... I don't top post - see either inline or at bottom.

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Tekkie


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Walter R. wrote:

Correctly sizing an A/C requires a number of measurements including insulation windows etc. A local HVAC man can do the calculation for you (it's called a manual calculation) and advise you of your options.
--
Joseph Meehan

Dia duit
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"Walter R." wrote:

You might want to poke around the web sites of a few mfgs to see if they have calculators.
Lou
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On Tue, 26 Jul 2005 01:07:24 GMT, in alt.home.repair RE: Correct

IMO, yes.
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