If your car's air conditioner isn't working, one possible cause is low oil levels. The compressor in the AC system is driven by the engine, and it depends on a sufficient level of oil to lubricate it. If the oil level is low, it can cause the compressor to seize up, preventing the AC system from working properly.
However, there are other potential causes of an AC system that isn't working, so it's important to have it diagnosed by a professional to determine the root cause. Low oil levels may not always be the culprit, but if it is, topping off or changing your car's oil can help get your AC system back up and running again.