i will use "common sense" to reply this one.
u turn on the AC and engine load increases
1)engine load increase=temperature rise
2)automatic transmission oil needs to cool down circulating through radiator
3)it means when the car is hot, transmission does not lock.
Have u ever changed ur honda's gear oil? Please buy 3 litrs of ZIC semi synthetic gear oil for auto transmission and get it changed. I hope that fixes the problem!