Is it useful to turn on AC when using car heater?

[VonJordan]

Heating only utilizes the internal heat circulation of the car and does not require activating the compressor. Therefore, to use the heater, you only need to adjust the air conditioning button and should never touch the AC switch. The function of the AC button: The AC button in a car controls the switch of the air conditioning compressor. The working principle of the air conditioning compressor is to compress and drive the refrigerant in the air conditioning refrigerant circuit, so generally, there is no need to turn on the AC button when using the heater. Therefore, the idea that many car owners have about needing to turn on the AC button when using the heater is incorrect. The impact of using the heater on fuel consumption: The principles of heating and cooling are actually quite different. The heater relies on the heat dissipation from the engine. There is a small fan in the engine compartment that blows the heat collected by the cooling system into the car. If the heater is not turned on, this heat will be discharged outside the car, so using the heater in winter does not consume fuel.

[VonLeonardo]

I used to think about this issue while driving. Turning on the AC when using the heater is indeed useful, mainly because it helps with dehumidification. The engine heats the air ducts to provide warm air, but when the weather is humid, the windows tend to fog up. Turning on the AC activates the compressor to remove moisture, instantly clearing the fog. This makes driving much safer with clearer visibility. For example, driving after winter rain, I’ve tried using just the heater, but it didn’t work—adding AC made a noticeable difference. Plus, the air feels drier and more comfortable. Of course, the compressor working does consume a bit more fuel, but it’s worth it for safety. In summary, I recommend keeping it on during fog-prone periods. The car’s air conditioning system is designed for this mode, so there’s no need to turn it off—let the car’s smart adjustments handle it. Don’t worry about it just being for cooling. After all, cars are meant to serve our driving convenience.

[ORiver]

When I first got my driver's license, I thought the AC was only for cooling. Later, while driving in the rain, the windows fogged up and I couldn't see the road clearly. A friend suggested trying the heater with the AC on, and it worked like magic! The AC compressor not only cools but also dehumidifies. As warm air comes in, the moisture goes away, and visibility becomes clear instantly. Now I've developed a habit of often using the AC to assist the heater during autumn and winter drives. It not only prevents fogging but also keeps the air inside the car dry and comfortable, making long trips more pleasant. Although the compressor running might increase fuel consumption, I haven't noticed a significant difference. Safety comes first, after all. Remember not to be afraid to use it—the car's air conditioning system is designed for various needs. Use it to enhance your experience, and don't get stuck in the misconception that it's only for cooling. Regular maintenance checks on the AC also keep things hassle-free.

[AniyahRose]

Turning on the AC when using the heater is absolutely effective, with the key benefit being strong dehumidification. When the engine provides warm air and humidity is high, the AC's dehumidification can quickly clear fog, enhancing driving safety. Here's my simple routine when driving: in winter, start the car, set the heater to the desired temperature, and turn on AUTO mode—the AC automatically dehumidifies to prevent fogging. On rainy days, manually turning on the AC also works. The downside is a slight increase in fuel consumption due to the compressor running, but the trade-off for clear visibility and comfort is worth it. It's advisable to use it flexibly based on the weather and avoid excessive usage to prevent waste. There's no issue when the air conditioning system operates normally.