I have a popup with the roof AC and it is comfortable well into the 90s (never had it out over 100) with MD and VA summer humidity. Now, the key word is comfortable, it won't freeze you out midday at the height of the summer heat, but it will give you a nice respite from the summer heat. I usually have to turn it down quite a bit at night. That said, I've found that the AC (and heat in cold weather) tends to want to stay in the box and not really get into the bunks (especially if you use the privacy curtains), so a fan (I like the little bunk end fans) is a necessity to spread the AC into your bunk area.