I'm in FL and have an 85 year old home with a somewhat poorly ventilated, small crawl space. Recently had the inside of the home tested for mold and levels were off the chart high. Humidity inside was >60% in some rooms.
60+% isn't great, but it is not awful either. Happy range is 40-60%. Florida is always super humid (was just visiting in laws there), so you are always going to have humidity creeping in.
I have a large (4 ton) relatively new (~3 yrs) AC unit which is probably oversized as it's cooling only about 1800 sq ft. I have 2 mini splits in rooms farthest from the AC unit. I say oversized as I've been told the problem is that the unit is cooling too fast and not removing the humidity. I just installed a Nest thermostat and the unit turned on/off 19 times in 24 hours - this seems excessive to me, but I'm no expert.
This is actually really good for an 85 year old that is usually poorly insulted. It will depend on differnce of outside temp and inside as well. Running 2-3 times an hour during heat of the day is common. Expect it to run about 15 mins on nice warm days and possibly non stop on 100+ degree days.
To make things worse the humidity levels from the AC supply ducts in the floor were incredibly high - almost 80% after the unit had shut off and the blower was still going. I was told that the flexible ducts could also possibly be compromised (perhaps a hole in them and thus exposed to outside air?). Another problem is that the flexible duct sits right on the ground which I'm sure is not ideal given the moisture it's likely exposed to. The ventilation of the crawl space is not ideal either.
Again, not that unusual. Humidity is modified by temp. You can have the exact same amount of moisture, but lower the temp and the humidity % will be much higher because the air can't hold as much moisture. In a humid climate I would expect the cold air (usually 40-50 degrees) from an AC to report a higher humidity than your ambient room, but once that air reaches ambient temp the humidity % should be same or lower.
Given your crawl space is in Florida, most of the year you probably can't get it lower than 80% because that is just what it is outside.
My question is this - should I go for a smaller AC unit and fix the problems with the ducts/ventilation and perhaps install some sort of barrier on the ground to block moisture? Or should I just bite the bullet and remove the unit and the ducts and just install splits in all rooms (4 heads total)? I've had conflicting advice from different AC contractors and it's very frustrating. I'm not so concerned about the cost - really just want someone to give me sound advice so I can get the problem fixed.
I don't think replacing your AC unit will magically fix humidity issues, more likely they are trying to make money off you. Maybe just look at some dehumidifier units? Look at possible insulation issues too.