That's precisely what I do in the summer, run the duct from the AC output to the chamber - still intersected by the ultrasonic humidifier to make sure the air is well saturated. I leave the AC going most of the day too since I don't like heat any more than the HL plants do! Nights don't get down to 50*F in August. August is likely the hardest month to get below 60*F at night even with the A/C. However, outside of mid June - mid Sept my window duct method is totally hassle free for me. In mid June hook the fan to the output of the window AC (in the window) and I'm done.
"Set it and forget it" is my motto, must be from sleeping thru all those infomercials!
The plants can deal with 60*F at night for those few months and come out all guns blazing as soon as the nights cool down in Sept and grow well until next June when they slow down.