Should the AC be turned on when using the heater?

[DiThomas]

When using the heater in the car, there is no need to turn on the A/C switch. This is because the warm air is generated by the heat from the car's engine and circulated into the cabin through the air conditioning system, without requiring the compressor to operate. Turning on the A/C not only fails to improve the heating effect but also increases fuel consumption. Correct usage of the A/C button: 1. The A/C button controls the on/off function of the air conditioning compressor. In summer, drivers need to turn on the A/C button along with the cold air setting to activate the cooling function, allowing cold air to circulate inside the car. 2. Drivers can turn off the A/C switch during acceleration or rapid acceleration because the air conditioning compressor is powered by the engine and consumes some of the engine's power. Turning off the A/C switch can prevent insufficient engine power.

[AlexaLee]

When using the heater, you usually don't need to turn on the AC button because the heat comes from the engine coolant. Turning on the AC will only make the compressor run idle and waste fuel. However, there's a little trick for driving in humid southern regions during winter: when you first start the car, the windows are prone to fogging up. At this time, turning on the AC can quickly dehumidify, and you can turn it off once the fog clears. I commute half an hour on the highway every day, and my personal experience shows that turning on the AC for two minutes before switching to the heater in winter keeps the windows fog-free throughout the trip. Also, be careful not to set the temperature too high; around 22 degrees is the most comfortable, otherwise the hot air blowing on your face can make you drowsy.

[DeLillian]

As a seasoned driver with over a decade of experience, I recommend not using the AC at all when turning on the heater. Think about it—the compressor is for cooling, and using it increases engine load and fuel consumption, which is completely unnecessary. The heater relies on the engine's water temperature, and the best effect is achieved by letting the car idle for five minutes before turning on the heater. Of course, exceptions apply in special cases, such as when the windshield fogs up severely on rainy days. In such situations, you can temporarily turn on the AC for ten minutes for strong dehumidification, which works three times faster than using the heater alone. Another tip: switch to external circulation mode when using the heater to prevent repeated fogging on the windshield—much more efficient than mindlessly running the AC.

[StMakayla]

Proper car usage habits are crucial. The warm air comes from the engine's residual heat and is unrelated to the AC compressor; turning on the AC actually increases component wear. However, I've noticed an interesting phenomenon in real-world usage: when cabin humidity exceeds 70%, relying solely on warm air for defogging the windshield proves ineffective. Briefly activating the AC dehumidification function for three minutes can quickly reduce humidity to comfortable levels. For winter driving, I recommend opening windows for 30 seconds of ventilation before starting the warm air with external circulation - this virtually prevents fogging. Additionally, replacing the cabin air filter quarterly reduces warm air odor issues by 80%.

[LaVera]

Technical analysis: The AC button controls the air conditioning compressor, with its primary functions being cooling and dehumidification. The heating system operates independently by directly utilizing heat from the engine coolant, making AC unnecessary in 90% of cases. However, precision electronic monitoring has revealed that when the temperature difference between inside and outside the vehicle exceeds 15 degrees and the humidity difference surpasses 40%, the windshield will inevitably fog up. In such extreme conditions, it's recommended to simultaneously activate both AC and heating for ten minutes to leverage the compressor for rapid humidity balancing. Under normal circumstances, setting the temperature to 24 degrees Celsius with heating alone is entirely sufficient and can additionally save 7% in fuel consumption.

[BriellaRose]

Actually, I rarely turn on the AC when using the heater in winter, since the compressor working consumes extra fuel. But once during heavy snow while driving with my family, the windshield completely fogged up after turning on the heater. I had to urgently activate the AC for five minutes before visibility was restored. Now my routine is: turn on the heater once the engine reaches normal operating temperature, and if fogging occurs, switch on the AC to dehumidify, then turn it off immediately once the fog clears. Also, avoid turning on the heater right after a cold start—wait until the temperature gauge reaches the midpoint. This protects the engine and prevents blowing cold air. It's recommended to keep the cabin temperature between 20-24°C, as this range is most comfortable for the body and helps prevent drowsiness.