Sit at one of the ends near the doors. Those seats tend to be noticeably cooler than the middle of the car in the winter. Doors are staying open at station stops and the vestibules are open to the elements so they cool off a little bit more. In peak summer, the middle seems to avoid the rush of hot air coming in at each stop.

Since you're in biz, not sure if the front set of doors by the engine open at station stops. It's a band-aid solution and longer stretches like WIL to BAL definitely make the heat more noticeable.