make sure its not pumped strait from the ac to the bottom were the plants are, cold will shock them. unless its not ice cold. 65 70 degrees is ok, colder than that and i wouldnt. i have a 400w mh/hps in my closet, its a 2 foot deep 3 foot wide 5 foot tall area, i only use heavy 4mm plastic sheats, black and clear, if you could get black and white its better. my i have no ventelation going into or out of my room besides a fan by the door and a fan blowing on my light, i try to keep the door open as much as possable but its right by my bed so its a no go at night. when its closed and the fans are on it gets up to 90 but with it open and fans going its about 80 to 85. i jumped the gun too and got the 400w system, but thats because i am going to be getting a new house and will have more space. a 150 or maybe even a 250w would have been great for this area... and would have saved me money... but ill just have to make due and rig up a screan hanging under my light for shade while the plants are young.
id say if its ok with the ac on in it then keep the ac on except durring the night cycle.