Does a Civic’s AC only work when the car is moving? Mine gets really cold if I’m moving, but blows hot when stopped at a light.
There needs to be air going through the condenser, which is the radiator-like thing that mounts in front of the radiator. Usually the electric fan runs when you turn on the AC, which provides the airflow, but I’ll bet your fan isn’t coming on with the AC as it is supposed to.
The refrigerant level might be just a little low. At idle it might not be building enough pressure.