Should the AC Button Be Turned On When Using the Car's Heater in Winter?
3 Answers
When using the car's heater in winter, there is no need to turn on the AC button. The warm air from the car's heater comes from the heat generated by the engine during operation, which is essentially a form of waste heat recycling. The working principle of the car's heater is as follows: after the engine's cooling system dissipates heat from the engine, the dissipated heat is blown into the car's interior by a fan to produce warm air. The method to turn on the car's heater in winter is to rotate the knob to the heating direction and turn on the fan switch to release warm air. The functions of the car's air conditioning system are: 1. To adjust and control the temperature, humidity, air cleanliness, and airflow inside the car cabin to an optimal state; 2. To provide a comfortable riding environment for passengers and reduce travel fatigue.
As a veteran driver with over a decade of experience, I initially thought pressing the AC button was necessary for winter heating, but later realized it's completely unnecessary. The car's AC button activates the compressor, while the heating actually utilizes waste heat from engine operation, much like residual warmth from a furnace. When the coolant temperature gauge reaches the midpoint, simply turn off the AC button and adjust the fan speed knob—warm air will naturally flow through the vents. Engaging the AC at this point would only waste fuel by needlessly running the compressor and placing extra load on the engine. However, there's one exception: when the windshield fogs up, using the heater alone is slow for defogging. Briefly activating AC with the heater for 2-3 minutes enables faster dehumidification to clear fog, after which the AC should be turned off. Additionally, for prolonged heater use, switching to external air circulation every half hour is recommended to prevent CO₂ buildup and drowsiness.
I remember when I picked up my new car, the salesperson specifically reminded me about the winter air conditioning usage. In winter, you don’t need to press the AC button at all when turning on the heater, unless you want to defog the windows. The principle is simple: car heating relies on the temperature of the engine coolant, just like a boiler heating water naturally; but the AC switch controls the air conditioning compressor. Normally, we turn off the AC, wait for the coolant temperature to rise, and then simply turn the temperature knob to the red zone. If you accidentally press the AC, the indicator light on the dashboard will turn on, and fuel consumption will increase by about 0.5 liters, like giving money to the gas station for free. When defogging, you do need to turn on the AC along with the heater, because the cold air can quickly absorb the moisture on the glass. I’ve found that it’s best not to rush to turn on the heater right after starting the car; wait until the coolant temperature gauge starts moving, otherwise you’ll just get cold air blowing out.
