Do you remember if it cooled from the start and has degraded or has it always been this way? Since this is your first summer its difficult to know a baseline. If it cooled early in the year but is hot now, then something like plugged condenser might be the problem. If it has always been this way, likely a system problem. Example - my BIL got a new (used, but new to him) tractor this spring. His son's operation has a lot of running tractors, either open platform or cab with inop A/C. He got this one because of his age (just turned 74) and can't handle the heat anymore. Midway through cutting first crop hay, he asked me if sweating in an AC cab is normal because it didnt' seem any better than open platforms or cab with all windows but the windshield missing. I checked and his compressor wasn't running. Defective pressure switch. Replaced it and now he's very happy. Something like this likely your problem, and considering its new, warranty.
I now have 3 Kubotas with A/C and had 2 others traded off for the ones I now have. Even though I live in Northern Minnesota where one wouldn't think A/C is all that important, we do have our days in the 90s. Having spent half my engineering career with AGCO and CNH, I can say that Kubota's A/C system is not the most powerful. Ag equipment cabs have so much glass area they need a lot more cooling than cars and pickups. Systems we had on Gleaner and Case IH combines were much larger than anything in a car - according to our A/C suppliers. On a 40 degree late autumn day in a combine, an operator still needs a lot of air conditioning when the sun is out while in a car you likely need heat.
