A/C Questions on temps, vents and more

OK - Some background. Bought my 2400 sq ft home in Feb, 2004. So, this is my first summer. In addition, it is my first home, so newbie alert on all sides.
The home has 4 stories. A garage/basement, where the A/C, heater, water heater etc are located. First floor is kitchen, D/R, L/R, etc. Second floor is 2 full baths and 2 bedrooms and Third floor is a loft/bedroom.
Vents are closed in the basement, the majority (not all) of the first floor and one of the two bedrooms on the second floor and all bathrooms. Vents are open in one bedroom and the loft.
When I turn the A/C on and the outside temp is lets say 85 degrees or higher, the A/C struggles to keep the home below 75 degrees. During the day, I have the thermostat set to 79 degrees and it easily holds at this temp. But, when I return home, it is set to bring the home to 75 degrees and the A/C runs all evening until I go to sleep, where the temp is again brough to 79 degrees.
Now, my questions:
1. When temp should the air be at the vents during A/C operation? How should I test this?
2. This is a fairly new home (less then 3 years old) so I assume the A/C units is not faulty. The filter is clean. What are other 'obvious' things to check?
3. It seems the air does not blow very hard in the upper floors. It blows very hard on the first floor, but poorly above. Any ideas?
Thanks much...
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Newer home and you think that they did it right........................... draw your own conclusion
Your condrundrum is that you think that the unit is properly sized. Call a local expert and ask them. Hard to see from here.
Anything ventured here will be pure speculation. We can not see/or know the whole situation. Not to slam you but WTF are the rest of the conditions your dealing with? Need an sooth sayer, go there. Want help spell it out in painful detail! I am not trying to be negitave, but with what you supplied it any help is an WILD ASS GUESS.
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Brian Tobin wrote: /snip/

Nominally the temperature difference between the return and supply registers should be in the range of 15-22 degrees. Use a thermometer. Note that this 'delta T' by itself doesn't mean much. You should check the temperature both at the return register and directly at the return plenum. If there is more than a 2 degree difference in the return air temperature at the plenum then I would suspect leaky or inadequately insulated return ductwork.

Not a good assumption. Also, how do you know if this is the right size unit? Did the builder / AC contractor provide you with a heat gain calculation worksheet (AKA "Manual J") and a duct volume calculation (AKA "Manual D")?

Assuming this is not a zoned system and that there are no dampers anywhere in the lines, this sounds like a duct design problem - ask for a copy of the Manual D showing how much airflow should be coming from each supply register, and ask the builder / contractor to measure the airflow at each duct to insure that it meets the design criteria.

You are welcome.
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Bolcking all those vents can restrict airflow enough to freeze your coil. Get a pro out . But first try leaving the fan on continously and letting the unit run longer, don`t set it back, minimal setbacks times less than 8 hrs may save Zero, you must make up lost cooling.
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m Ransley wrote:

Citation, please? It is my understanding that ANY A/C setback (except one that causes short cycling) will save in electrical power.
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