Engine oil and oil filter require regular replacement:
we recommend every 3000 miles or every 12 months whichever comes first.
If your Air conditioning is no longer working the chances are it needs an re-gas. Some cars require a re-gas more frequently than others.
Engine coolant is absolutely necessary for the engine to function without damaging itself. You should check this frequently and book in to have this flushed and refilled at regular intervals.