Yes, it is possible to start an AC unit without a pre-season maintenance service, but it's not recommended. Pre-season maintenance is important because it helps to ensure that the unit is running efficiently and effectively, and can also help to identify any potential problems before they become major issues. Without regular maintenance, an AC unit may be more prone to breakdowns, which can lead to costly repairs or even replacement. Additionally, a poorly maintained AC unit may not cool your home as effectively, resulting in higher energy bills. So while it's possible to start an AC unit without maintenance, it's always best to schedule a pre-season maintenance service to ensure that the unit is running at peak performance.