The Necessity of Turning Off the Air Conditioner Before Turning Off the Car

When it comes to whether you should turn off the air conditioner before turning off the car, opinions vary. Many drivers, including your husband, believe that turning off the air conditioner before starting the car can help reduce engine load. This article aims to clarify the impact of leaving the air conditioner on versus turning it off for both older and newer vehicles, focusing on engine load, fuel efficiency, and comfort.

Influence on Engine Load

When you start a car with the air conditioner (A/C) on, the compressor engages, which adds extra load to the engine. This additional load can make the engine work harder during the initial start-up, potentially leading to more wear and tear, especially in older vehicles. For newer vehicles, the impact may be less significant due to improved engineering.

Affect on Fuel Efficiency

Leaving the A/C on during start-up can lead to slightly higher fuel consumption. This is because the engine must handle both the load from the A/C compressor and the normal start-up load. However, in modern vehicles, the computer will manage the compressor's engagement based on the engine's demand, which can mitigate some of this extra load.

Comfort Considerations

Some drivers prefer to turn off the A/C before shutting off the car to avoid a blast of cold air when they start the car again, especially in hot weather. This preference is purely for comfort and may not have a significant impact on the vehicle's performance.

Modern Vehicle Technology

In many vehicles, particularly those manufactured from 1990 onwards, a circuit opening relay is used to cut off power to the A/C compressor’s magnet clutch. When you turn off the car, the relay automatically cuts off the power, making it unnecessary to manually turn off the A/C.

However, leaving the fan running for a couple of minutes before stopping the engine can help dry out the A/C evaporator. This can prevent the "AC just turned off" smell, which many car manufacturers experience due to moisture buildup in the evaporator, potentially leading to mold growth.

The engine in modern cars is designed to start with the A/C compressor clutch already disengaged. The ECU (Engine Control Unit) will engage the compressor only once the engine is running, meaning it is not harder on the engine to start with the A/C on.

Conclusion

While it is not strictly necessary to turn off the A/C before shutting off the car, doing so can be beneficial for engine longevity and fuel efficiency, especially in older vehicles. For newer cars, the risk is minimal, and the impact on the engine is negligible. In any case, the additional benefit of leaving the fan running for a couple of minutes can help maintain the A/C system's cleanliness and prevent unpleasant smells.

Keywords: engine load, fuel efficiency, air conditioning