So, it's a closed rig, I guess to avoid dust?
If the room temperature is high, a closed system has more consequences than advantages. An AC will definitely work to your scenario, though.
If the room temp is fine, it's definitely the internal airflow. Either your fan sucks or
positioning problem.
Another way is to try to lower down room temperature! It actually helps a lot for closed rigs
Like this for example, you can install an AC if you're using a closed rig casing.