Yes you can use your air conditioner in your room and it naturally is a dehumidifier so you probably dont need to use both a dehumidifier and an air conditioner. The thing is you can't see bad humidity conditions for your health. Just because you dont see mold doesn't mean your health is not effected. You should get a humidity gauge for your room and for the terrarium. Because both are going to be a lot different. First and foremost get your room to stay at or below 55% humidity. Next get your terrarium humidity at 55%. The easiest way that I have found to do this is to place a bed sheet over the terrarium in order to maintain a consistent 55% humidity. It will also keep your temperature more consistent. I hope you are not using a heat lamp. If you are using a heat lamp than you cannot put the bed sheet over your terrarium. I hope this helps. For now I would run the air conditioner or dehumidifier in your room until you get your humidity gauge.