grow room problems

i started a grow room 3 foot by 3 foot and 6 foot high . i have a 400 watt light also have a exhaust fan running to the outside and a intake fan that i am pulling some air in from outside . i also have a vent running into the room that is hooked to a a/c unit . and i have been keeping the room around 75 to 77 . i also have a co2 tank and been hitting the room a few times a day . my problem is the plants are drying up the leaves where nice and green and then i put them in the room and they slowly started to turn yellow and die off . could this be because i am not pulling enough outside air into the room or could it be something to do with the co2 . i had some plants outside in the yard and they where doing great getting big and nice and green when i moved them into the room the slowly started to turn yellow and die off any clue what i am doing wrong here . should i get a bigger intake fan and pump more outside air in ...please help i might have to start over .....thanks for your time and any help on this

Lose the Co2 just for process of elimination reasons. It could be the drastic change in enviorment. I'm guessing but I bet your humidity changed drastically with the pumped in a/c as well as the closed in conditions.