Should You Turn on the AC When Using the Heater in a Car During Winter?
3 Answers
In winter, it is generally not necessary to turn on the AC when using the heater. However, on rainy days when fogging is likely to occur, turning on the AC button can not only blow out hot air but also help defog the windows. Therefore, you may choose to turn on the AC button in rainy conditions. Apart from its cooling function, another important role of the car air conditioning system is dehumidification, which also helps remove frost, fog, and condensation from the windows. The main principle is that when warm, humid air flows through the evaporator, the heat is absorbed, and water droplets condense on the evaporator, thereby reducing the humidity inside the car and aiding in window defogging. The AC button controls the air conditioning compressor. In summer, when using the air conditioner, you must turn on the AC button to activate the cooling function. However, the heater utilizes the car's internal heat circulation and does not require the air conditioning compressor to be activated. Therefore, to use the heater, you only need to adjust the air conditioning controls without turning on the AC switch.
After driving for so many years, I usually turn off the AC when using the heater in winter to save fuel, since the AC engages the compressor, consuming more fuel without warming the air. However, when severe window fogging occurs, I turn on the AC along with the heater because it quickly removes moisture and clears the fog—safety first, as poor visibility is dangerous. Normally, the heater uses engine waste heat, which is sufficient for warming without extra complexity. I recommend setting a higher temperature at startup to dehumidify, then turning off the AC once the car is warm—this saves fuel and ensures comfort. Getting used to this simple routine is easy. Regular maintenance of the AC system prevents unnecessary energy waste, saving money and ensuring safety. In short, defogging is key; otherwise, using the heater alone is fine. Adjusting driving habits to different weather conditions is essential.
I'm an energy-saving enthusiast. In winter, I never turn on the AC for heating unless absolutely necessary for defogging. Turning on the AC activates the compressor, increasing engine load and fuel consumption by 5-10%, which is neither cost-effective nor resource-efficient. The heating system itself relies on engine heat, so just turning on the fan to blow warm air is sufficient—no need to waste extra electricity. With proper cabin environment control, window fogging can be minimized by simply closing windows or using recirculation mode. For daily use, I opt for ventilation mode to save fuel, reducing carbon emissions and being eco-friendly. Avoiding prolonged AC use also extends the compressor's lifespan and minimizes maintenance hassles. If humidity is high and dehumidification is necessary, a brief AC activation is acceptable, but long-term use is not recommended. A simple strategy is to set the temperature slightly lower to avoid dryness issues, ensuring both safe travel and economy. Remember the core principle: when heating, the AC can be turned off, with fuel efficiency as the priority. Cultivating good habits is beneficial for both your wallet and the planet.
