Okay let's go back to plant basics 101, cos either you don't know or don't understand.
There's 4 basic building blocks for plant growth and photosynthesis - light, water, co2 and nutrients. If any of those 4 basic building blocks are deficient in any way, or the plant doesn't get enough of them, the plant will either die or won't grow properly. A plant uses up the co2 in the air around it's leaves in a few minutes, if this isn't replaced every few minutes the plant will stop photosynthesis, slow down it's metabolic rate, become stunted and eventually die.
This is why you need to replace the air in your grow chamber once every 3 minutes for healthy plant growth and photosynthesis. A ventilation fan performs two primary functions in a plant grow chamber 1) To ensure a constant flow of c02 rich air from the outside via negative air pressure within the grow chamber with the fan extracting stale, co2 spent, warm air and sucking in new cool fresh air via the passive air vent; 2) To control temperatures and heat build up by extracting hot warm air and pulling in fresh cooler air.
I don't really see how an air conditioner (unless it's vented to the outside) can help you achieve point 1, although it would probably achieve point 2 - to control temperatures.
Contrary to popular belief, it's actually better to intake air from inside a house, flat or dwelling, than from outside fresh air because air in a house where people live will have far higher concentration ppm of co2 in it than that brought in from outside the house for the simple fact that humans exhale co2.
Do not underestimate the importance of bringing in fresh co2 air from outside the grow chamber.
