How to Find and Stop a Draft
Drafts are much easier to find during the winter. If you don't pay for heat, but will pay for AC, it's a good idea to take some time and find the draft on a colder day. First, identify the area of the house that is cold. On a windy or very cold day it might be immediately apparent where the draft is coming from. If it's not, check for the usual suspects: windows, doors, holes for wires going into the wall. You should be able to feel the cold air entering from the source of the draft.
Once you find the draft, work to stop it. If the draft is coming from underneath a door, you can get a draft stopped to fill the gap between the door and the floor. If the draft if coming from a window, make sure the window is fully closed and locked. "Do it yourself" options for eliminating the draft include (1) using weatherstripping, (2) using foam tape or (3) hang insulating curtains. If it is coming from the door, you may also consider purchasing a door snake to block the draft. If you can't find it or it or it requires more work than you are willing or able to perform, contact your landlord about repairs. Keep in mind that you should always contact your landlord before making any permanent changes to your unit, even if you think it is an improvement.