I had a two story home on S Florida. Two ton units on both floors. The second floor could never get cool enough unit I replaced the second floor with. 2.5 ton and during the heat of the day it might make it down to 75 but it would run most of the day until the evening. I had the home for 26 years.
The best trick is you need to balance the thermostats. The first floor unit needs to be set 2 or 3 degrees cooler. What happens is we all know that hot air rises. At certain temps the second floor can actually cool the entire home and if both thermostats are set the same temp the first floor ac shuts off. Now all the heat from the first floor continues to rise and the second floor unit now tries to cool the entire home thus run all day.
Set the first floor thermostat, to start at 3 degrees cooler. Now the first floor will do it’s fair share on the heat load. The second floor will always be warmer and yes it will run most of the time when the sun is up.
You mention 800 sq ft. I’m assuming that’s the second floor only. What’s the entire home?
Another problem I had was after I had the roof replaced, the ridge vent did not work as well as the original ridge vent. On the summer days I could actually feel the heat radiating down from the attic space. Better ventilation and or attic insulation will help big time.
I sold the home and the first thing the new owner complained was the second floor ac wasn’t working, it was a brand new unit. He set the first floor thermostat too high thus the first floor ac would hardly run and not take it fair share of the heat load b
Your problem is not the Trane unit. Air temps you mention are good but there is not enough volume of cool air. It the unit was not performing the gauges would show incorrect pressures.
Right now the entire east coast is high in humidity and it takes more energy to wring the air of water.
I now have a different two story home on Orlando with one 3.5 AC heat pump on the second floor. Seer 16. A well insulated home, windows tinted, the south facing front porch shades 72 sqft of windows. No problem keeping the both floors cool but the second floor is always warmer and will always be warmer.
I have a Honeywell smart thermostat and it has a fan setting “circulate”. At a minimum the fan will run 35 minutes per hour just circulating the air. It allows the air from the first floor and warmer air from the second floor to mix thereby keeping the temp of both floors more even.
My son lives down the street in a two story home with two heat pumps. 3200 sq ft. 2 ton first floor, 3 ton second floor. No problem keeping the temp down but summer time the ac will run a lot. The home has the same insulation and same builder built in 2007.
You mentioned compressor in the garage? What?
What’s the temp of the first floor, second floor and where is the thermostat.
How old it the home?
Attic and walls well insulated?
How many windows (sw ft of glass$ faces south.
Is this your first central air for this home?