Should the AC be turned on when using the heater in a car?

[DeKendra]

When using the heater in a car, the AC should not be turned on. The method to use the heater is as follows: 1. After the car has been running for 5 to 10 minutes and the water temperature has risen to normal temperature, you can then turn on the car heater; 2. Adjust the car air conditioning circulation mode to internal circulation; 3. Switch to the car heater mode, which is the red zone; 4. Adjust the car air conditioning gear to a suitable position and adjust the direction of the car air vents. Precautions for using the heater: 1. Do not turn on the heater immediately after starting the car; 2. If the windows fog up, increase the heater fan speed; 3. Do not press the AC button; 4. Set the circulation mode to internal circulation; 5. Adjust to a suitable temperature.

[SpencerMarie]

I used to wonder whether to turn on the AC switch when using the heater. After driving for over a decade, I realized there's absolutely no need to press the AC button. The car heater utilizes waste heat from the engine—simply put, once the engine warms up after starting the car, the fan blows out hot air, completely free and fuel-free. The AC controls the air conditioning compressor, mainly used for cooling or dehumidifying during humid weather to defog. If you keep the AC on while using the heater, it unnecessarily increases engine load and burns more fuel, which isn't worth it. Of course, if the car feels stuffy or the windows fog up, turning on the AC briefly can speed up dehumidification for clearer visibility—just turn it off afterward. For daily use, simply adjust the temperature and fan speed, and use the recirculation mode to make heating more efficient. Regularly checking the cooling system can also prevent issues, avoiding sudden malfunctions that affect driving comfort.

[RiverDella]

When I first started learning to drive, I also asked my instructor this question and later figured it out: You don't need to press the AC button for heating. The heater relies on waste heat from the engine to warm the air, and hot air comes as soon as you turn on the fan, while the AC button activates the air conditioning compressor for cooling or dehumidifying. In winter, if you turn on the heater with the AC running, you're just wasting gasoline because the compressor consumes extra energy. However, when your car windows fog up or there's an unpleasant odor, using the AC along with the heater provides better dehumidification, clearing the glass in seconds. Many new cars now come with smart climate control systems that automatically decide whether to activate the AC, so you can usually just turn it off when manually adjusting. Get into the habit of paying attention to air circulation inside the car, using the external air circulation to prevent stuffiness—this saves fuel and keeps you at ease.

[VanSophie]

After years of car repair experience, I've found that using the heater without turning on the AC is a good practice. The heater relies on engine heat transfer, where the fan blows warm air is sufficient; the AC compressor operates independently for cooling or dehumidification. Turning on the AC only increases fuel consumption and engine load, making it completely unnecessary and a waste of money. Unless there's an emergency like window fogging, using the AC for dehumidification allows for quicker visibility on the road. It's recommended to regularly check the cabin air filter to maintain smooth system operation for more efficient performance.

[LaKinsley]

I always think about fuel-efficient driving, and turning on the heater without the AC button is definitely the most economical. The heater uses free engine heat and only relies on the fan, saving effort and not consuming fuel; pressing the AC button activates the compressor, which burns more gasoline unless you need to quickly defog or dehumidify for a few seconds before turning it off. In cold weather, opening windows can easily cause fogging, so turning on the AC for dehumidification is important for safety, but usually, you can just raise the temperature, turn off the AC, and use the external circulation to ventilate and avoid stuffiness in the car. Remember, maintaining your car's air conditioning system well can save a lot of trouble and be more environmentally friendly in the long run.

[Keegan]

Driving safety comes first when it comes to using the heater and AC button: Normally, there's no need to turn it on at all. The heater relies on engine waste heat, which is simple and reliable—just adjust the fan speed. The AC system is designed for cooling and dehumidification; using it unnecessarily increases fuel consumption. However, it's crucial to note that when the windshield fogs up and visibility becomes blurry, immediately turning on the AC along with the heater for dehumidification can quickly improve the situation and prevent accidents—this is a critical practice. At other times, keep the AC off, use the recirculation mode, let the warm air circulate, and adjust the temperature appropriately. Developing good habits not only saves energy but also enhances comfort. Maintain your vehicle's air conditioning system by cleaning it regularly to ensure optimal performance.