AC stands for air conditioning. Most cars today have an air conditioner in them. If you have ever tried to start your air conditioner in your car with a car off, you may be aware that the air conditioner did not turn on. That is because air conditioner needs the engine running in order to work. If you believe your air conditioning unit in your car for a long time then it will burn a lot of gas. This is because the engine makes the air conditioning unit work.
Also, it takes gasoline or fuel to run the engine. Therefore, you should conserve your air conditioning unless you really need it because it eats up gas. If you are low on gas you need to turn off your air conditioning.