You should call out your installer again. I think your system performance is poor. When it's 78 outside, my heat pump is kicking out air in the low 50's within a few minutes.

Sounds pretty good to me. High humidity and I don't buy 98%, kills cooling capacity since the units are working so hard on humidity removal. Dropping 6° in 4 hours with high humidity isn't bad at all. Since heat rises, the upstairs will take longer to cool since heat from downstairs is going up and cool air from the upstairs unit is going down.

As for temp drop, needs to be measured over the coil. Measuring at the outlet & inlet grilles only tells part of the story especially with attics where duct heat gain affects it. With high humidity, 12-15° drop over the coil isn't out of line. With low humidity it is more like 20° split. Usual problem is installers not properly setting the blower speed. Most just leave the unit on high. Proper way is take duct static pressure (few know how to do this) and consult the blower chart for the unit and set speed for no more than 400 CFM per ton. On Trane XR80s with 036 blowers, that is often low or medium low for cooling.

Thank you both for your comments.

Two days after the install the systems were not cooling. When I spoke with him about the issue, he said my settings for Leave & Return temperature are more than 5 degree, and everything in the house were hot so it would take time to cool. It turned out the downstair water line was pinched, and the attic water line was clogged. So both systems turned off the condenser.

After that fixes both systems got cooler, not cold. Not as cold as my old systems.

It had just stopped raining, so I assumed the humidity was at 98%. For one time I saw the weather report right after the rain and they reported that figure.

Tested it again last night at 920pm, with 97 degree outside, and the air vent registering at 66 degree.

The installer is coming back out tomorrow, and again he does not believe me it is an issue. He reminds me again about the setting being too far apart and everything in my house are hot. Well, I have not add any new furnitures or change anything in my house, why days old systems are feeling warmer than 19 years old systems?

On the internet I read this in several places about testing the performance:
Use a household thermometer, measure the temperature of the discharge air from the register and the temperature of the return air at the return air grill. The supply air temperature is directly related to the return air temperature. Equipment is designed for approx 16 to 20 degree temperature difference.

So why my systems air vent can only put out 66 degree, when the outside temperature is at 78 and my inside air is at 75 degree?!

The air does seem to blow out of the air vents stronger than before, maybe you are correct about being the blower is too high and that is the reason the air is not cold enough?!

Making more sense now. You may want to play with leaving the thing set to maintain a constant temperature (humidity) and see how that affects your performance. Did you do all this setback stuff with your old system?

If you're setting your system to allow a large temperature increase in your absence, the subsequent cool down can be rough. Your interior humidity is probably increasing with the temperature. Air conditioning doesn't like interior humidity. It initially works to get it back down before it can cool most effectively.

Go pick up a digital thermometer/hygrometer combination that logs min and max readings and set it on your thermostat. This will give you a better picture. They aren't very expensive. Maybe $20-30.

Digital thermometer/hygrometers start at $6.47 at my local Wal-Mart. They also have more complex models up to $20+. You can find them in WM in the aisle with the air filters (I wouldn't advise asking a WM employee for a hygrometer!).
You can also find models at Kmart, Lowes, Home-Depot etc.

We bought several of the $6-$15 models and put them throughout the house and in the garage and crawl space after having a lot of moisture problems last year. They are a great investment, and even if they are a few %/F off, you will get a better idea about humidity conditions in your house, which you can address if the need be.

A 9F degree split is POOR performence in any condition. Call the installer back. 75F in 66F out? Sounds like it is undercharged or air flow is incorrect for the charge.

Thanks for all your advices.

Turn out the downstairs AC unit was not fully charged, and the new roof we got last year in November did not work well with the upstair AC unit.

I wrote to Trane and they had a local technician to call me. Then he instructed my AC installer to call him to get more information on the installations. Both of them felt I needed a power vent.

The roofing company salesman told us to replace the two power vents with ridge vents. He said the ridge vents would worked better.

I called the roofing company back and the owner came out within two days of my call. He said the way my roof was pitched it could use a power vent. He gave us an excellent deal to install a powerful power vent by the AC unit. Saved us $200 if we were to hire someone else.

The power vent is working great and is able to keep upstairs cool.

Thanks again!!

p.s. If you live in metro Atlanta area the roofing company I've used is Atlanta Roofing Specialist in Marietta. I am real impressed with their customer service and integrity. The 'afterwards' service is what makes a company stands out from the rest.

mym2222 you must live in west cobb and got a roof from ins company with hail damage. you must live somewere near due west road,mars hill road or brookstone. i also got a new roof and so did 5000 other homes. i used classic roofing of marietta who were also awesome.i'm also very diasppointed in the ridge vents.i had no vents before and thats why i really wanted a new roof but i see no difference in anything with the ridge vents. atlanta roofing specialist has the red signs. some of these roofers made 500k or more in 5 months with these hail storms. so how much did the power vent cost you?what type monthly did it save you on summer air bills?

High humidity and I don't buy 98%, kills cooling capacity since the units are working so hard on humidity removal.

funny, day before yesterday the humidity here was 94%. and it had not rained in a couple days. even that rain was only a small sprinkle. right now the humidity is only 35%, a rare occurance around here.

but yes, when the humidity is high the unit has to work harder to remove it first. a low charge means real poor performance. my new Trane was overcharged and had the same issues.

Apologize for such a late reply. Thanks for the information about the humidity could reach 94% on a sunny day!!

I live in E.Cobb and the roof was 20yrs old. So it was a maintenance reason for the re-roofing.

I think the savings was pretty good for us. The power vent improved the AC performance. For the hottest month (AUG)we had in Atlanta our electric bill was only $129.64. We kept it at 76 degree with two systems, 3200 sq.ft. house. I remember in the past the most expensive electic bill I had payed was around $170. Jul $80.90TY/$120.6LY; SEP $67.68TY/$65.80LY.

I feel Atlant Roofing Specailist is a great company to deal with. That is based on their excellent customer service. Anyone/company can delivers a good sales pitch or a low price, but the 'afterwards' customer service will reveal the true nature of the company. They only charge me $100, labor and part. Even my AC tech was impressed. He said the person he would have referred me to would cost us at least $350 for parts and labor. Not only was the price low the guys from Atlant Roofing Specialist showed up ON TIME!!

Thanks again for all your assistance. Wish a Merry Christmas and a Happy New Year!!