Do You Need to Turn on the AC Switch When Using Car Heater?

[IvanMarie]

You do not need to turn on the AC switch when using the car heater. Introduction: The heating system in a car does not require the compressor to work for heating. Instead, it directly uses the hot air from the engine's cooling system as the heater. Therefore, there is no need to turn on the AC switch when using the heater in winter. However, when using the heater in winter, you should not keep the windows closed for too long, as the engine produces a large amount of harmful gases, such as carbon monoxide, which can cause poisoning or even death. Thus, it is important to remember to ventilate the car when using the heater in winter. Other Functions of the Car Air Conditioning System: The car air conditioning system also has other functions such as internal circulation, external circulation, and air supply mode, which should be used according to different situations. For example, when the air quality outside the car is good, you can use the external circulation mode to refresh the air inside the car, and vice versa. Additionally, if the windshield becomes foggy, you should turn on the defogging function to restore clear driving visibility. Different situations require different modes.

[IanRose]

I think whether to turn on the AC switch when using the heater in winter while driving is a topic worth discussing. The heater mainly uses waste heat generated by the engine, which is blown out as warm air through the fan, so normally there's no need to turn on the AC switch at all. This is because the AC switch activates the air conditioning compressor, which is primarily designed for cooling. Turning it on frequently will increase engine load, leading to higher fuel consumption—possibly an extra 1-2 liters per 100 kilometers—and also accelerate wear and tear on the compressor components, raising maintenance costs. However, on humid days, such as after rain or snow when the windows fog up severely and obstruct visibility, turning on the AC along with the heater can quickly dehumidify and dry the air, avoiding safety hazards. I adjust accordingly: normally, I turn off the AC when using the heater to save money and be eco-friendly; when there's heavy fog, I briefly turn it on to defog the windows and then turn it off to maintain safety. This way, I can balance economy and comfort.

[OAlex]

Through years of driving experience, I believe whether to turn on the AC with heating depends on practical needs. The warm air comes from engine waste heat and doesn't require compressor assistance at all. Turning on the AC actually increases fuel consumption, making the fuel gauge drop faster, which is detrimental to long-term vehicle maintenance. The only exception is when there's high humidity inside the car or fogged-up windows - then turning on the AC can dehumidify and ensure clear driving visibility. I always check the weather before starting the car: in dry, fog-free conditions, I turn off the AC for heating to save fuel; on humid days, I briefly turn it on for a few minutes to defog before switching it off. This habit has helped me avoid many accidents while saving significant fuel costs each month - making driving both safer and more economical.

[ORyder]

For driving safety, I noticed that turning on the AC switch is not necessary when using the heater, as the warm air comes from the engine's residual heat. Activating the compressor only increases fuel consumption and wastes resources. However, when windows fog up and obstruct visibility, turning on the AC for dehumidification can quickly solve the problem and prevent accidents. On cold days, I first turn on the AC heater to clear the fog, ensure clear road conditions, and then turn it off. This approach protects visibility, is economical and practical, and makes the driving process more reassuring, especially for family members—simple and effective.

[JudeRose]

From a fuel-saving perspective, turning on the AC switch when using car heating is simply a waste of money. The hot air comes from free engine heat, while compressor operation increases engine load and may raise fuel consumption by about 10%. The key to long-term fuel savings is turning it off. Only briefly activate it on humid days to dehumidify and dry the air to prevent fogging, then immediately turn it off to maintain efficiency. I operate this way too, saving fuel costs and reducing maintenance hassles.