It runs half the time, so you want to make it even larger?
A 2 ton system running 60 minutes per hour is more efficient than a similar 4 ton running 30 minutes per hour, especially with dealing with humidity.
Upsizing AC for efficiency is like taking the four cylinder out of your Focus and dropping in a V8 to save on gas.
Your 98% design conditions in Tampa are 32° C dry bulb, 25° wet bulb.
Ideally, your A/C should not run more than 100% of the time to maintain your desired temp in design conditions, so a 4 ton running 80% of the time is better than a 3 ton that can't keep up, and a 3 ton / 4 ton two stage unit running full time switching between stages is better than a 4 ton cycling on and off. I wouldn't be surprised if you could drop down to a 2.5T or 3T, but I don't know what your duty cycle is at peak afternoon temps. You could try a 4T two stage, or better yet, a variable speed inverter drive condenser.
If you don't want to slightly gain heat in the 2% of the time that design conditions are exceeded, your 99.6% design conditions are
34°/25°. But that's not necessary, because 76° indoor temp with the AC running 100% of the time is going to be very low humidity and more comfortable than you'd expect.
I'm surprised your cooling design temps are so low, only 2-3°C above Lansing, MI. Must be a coastal thing. Are you far enough inland that Tampa design temps don't apply to you?
If your A/C runs less than 80% of the time maintaining 74°F in the afternoon sun on a cloudless 90° day, strongly consider buying something like this and putting a thermostatic expansion valve on the indoor coil if you don't already have one.
The two problems with oversized A/C:
1. It doesn't dehumidify as well (major consideration in much of Florida).
2. You need a big duct system to handle the airflow needs (about 400cfm per ton).
The good news is that a 3 ton condenser on a 4 ton indoor coil is more efficient than a balanced 3 ton system (higher EER/SEER) if you downsize your outdoor unit.
The bad news is that the 3 ton coil would have run colder and dehumidify better. But you can gain latent heat capacity (dehumidification) by reducing airflow. 350CFM/ton dehumidifies better than 400CFM/ton.
For me, I almost never run AC in peak temps. If it's over 73°F, I feel a bit warm sleeping under a sheet, so I set the AC to 72-73 in the evening/nighttime. In the morning, I try to do most of my air conditioning when it's colder outside than inside and the AC is most efficient. If it's 55° when I get up and going to be 90 in the afternoon, I might cool to 68° in the morning and let it warm up to 78 during the day, then drop it to 76 in the early evening and 72 at 9pm. If it was 80° at night, I'd probably have to do things a bit differently.
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