There are a few signs that it's time for one of these tasks. For example, if your car's oil looks dirty or smells burnt, it's time for an oil change. If your car is having trouble starting or the battery is draining quickly, it's time to replace it. If you notice that your car's heating or air conditioning is not working properly or is blowing out hot or cold air unevenly, it's time for HVAC maintenance. Paying attention to these signs and addressing any issues as they arise can help keep your car running smoothly and avoid costly repairs down the road.