One room that's always hotter or colder than the rest of the house is usually a sign that something isn't working evenly. Sometimes the problem is simple. Other times, it's an airflow or duct problem that's been there for years.
By October, most people are ready to be done with the AC. In Los Angeles, some of our hottest days can come in the fall. We've been doing this work in LA since 1981, and October is still AC season here.