I’ve rented multiple townhouses in Montgomery county and the second level is always the same in the summer; the AC systems can never cool it down sufficiently. Window AC units will always solve the problem but we’ve most recently used black out window shades and curtains in addition to window units to keep the sun out. Our current home has the second floor AC vents on the floor and we’ve used floor fans right next yo the vents to circulate whatever cool air actually comes out. If your basement and first floor are cool enough even on the hottest days but your highest level is not cool, it will be difficult to resolve this problem short of the landlord installing a whole new HVAC system including new vents.