Yes, idling your car with the air conditioning on, even at a low setting, can consume a significant amount of fuel over time. When your car's engine is running, it continues to burn fuel to keep the engine running and power the accessories, such as the air conditioning system, lights, and electronics.
The exact amount of fuel consumed while idling depends on various factors, including the engine size, fuel efficiency of the vehicle, the outside temperature, and how long you keep the car running. As a rough estimate, idling your car with the AC on can consume between 0.1 to 0.5 gallons (0.38 to 1.89 liters) of fuel per hour.
If you're looking to conserve fuel and reduce emissions, it's best to turn off your engine when parked for an extended period, especially if you're not actively using the air conditioning. In situations where it's feasible, consider rolling down the windows or using the car's ventilation system without the AC to save fuel and reduce environmental impact.
Additionally, modern cars often have start-stop technology, which automatically shuts off the engine when the vehicle is stationary and restarts it when you release the brake. This feature helps save fuel and reduce unnecessary idling when appropriately utilized.