This is DEFINITELY not a DIY. I want to know what my reasonable options are. But first, the details.
We have a 3100 sq ft single story house (9 ft ceilings) in east central Fla. The house was built in 2008. White Aluminum roof, double pane single hung "hurricane proof" vinyl windows, sealed (unconditioned) attic. The house faces north. The east wall has no direct sun exposure (massive sea grapes). The north and south walls get no direct sun in the summer ( 2 foot eaves). The west wall gets direct sun for about 3 hours.
We have two identical Carrier Air Conditioners. The Outdoor Units are Model 25HCA336A0030010. The Indoor Units are Model FX4CNF042. The thermostats are Honeywell TH6110D. About 3/8 of the house is on the "North System". The remaining 5/8 of the house is on the "South System" (where most of the heat generating stuff is located). The contractor who designed and installed the two systems ASSURED me ( on several occasions) that the units were properly sized (I did not know about load calcs and never saw any). The original ducts were so poorly installed that my builder forced the ducts to be removed and "properly" installed. During the "dry-in" phase, I noticed that the compressors only ran ~5 minutes and one unit "rattled". The tech who came out to fix the rattle told me "all Carrier's run short on-cycles".
We moved in in late 2008. In the summer of 2009 we kept the house open most of the time so it was hard to evaluate how the AC was running. In 2010 my wife said the air from the ducts was "cold" and the humidity stayed in the high 50% region. Several times we turned down the thermostats to 60 (we normally run the temp at 78) and left the house for several hours. Humidity dropped for a while.
Last year I decided to try and determine how our AC's were working. On 7/12/2011 I measured the run times of both AC Systems. The outdoor temperature varied from 75 to 94 degrees. The outdoor humidity varied from 65% to 94%.
The North AC ran 45 times for a total of 3 hours and 24 minutes. The minimum compressor on time was 4 minutes (5 times) and the maximum run time was 5 minutes 30 seconds (2 times).
The South AC ran 52 times for a total of 4 hours and 44 minutes. The minimum compressor on time was 4 minutes 30 seconds (4 times) and the maximum time was 6 minutes and 30 seconds (3 times).
Both thermostats were set at 78 degrees. The indoor humidity was 52% to 55%.
I talked to my contractor and told him that I wondered if we were "over air conditioned" because the cycle times were short and the humidity was high. My contractor talked to the AC company (they won't talk to me) and was informed that in no way were we "over air conditioned" and if we didn't like the humidity, they could install a dehumidifier.
This spring we bought a Frigidaire FAD504DUD 50-Pint Dehumidifier. It fills up twice a day (100 pints of water) and the indoor humidity varies from 44% to 47% regardless of the outdoor humidity. Other than it being noisy and having to empty the bucket, we are satisfied with the comfort.
Now that you are "bored to tears", I have several questions.
1. Are the compressor cycle times typical for these Carrier Air Conditioners?
2. If we are "over sized" is there any way to "de-tune" these Air Conditioners ?
3. Would a humidity assisted thermostat help?
4. What criteria would I use to select a new air-conditioner contractor ?
Thanks for any suggestions.