Should the AC Button Be Turned On When Using the Car's Heater in Winter?

[LauraRose]

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.

[OwenDella]

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.

[LeJude]

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.

[OAngela]

As a car owner who treats my vehicle as a companion and focuses on maintenance, I pay special attention to the proper use of the air conditioning in winter. When turning on the heater, don’t press the AC button! This not only wastes fuel by making the compressor run idle but may also lead to insufficient lubrication of the refrigerant oil inside. Remember, the heater utilizes waste heat from the engine, similar to how a home radiator works. It’s recommended to wait until the coolant temperature gauge reaches around 90°C before adjusting the fan speed, and setting the temperature above 22°C is most comfortable. The only time to use AC is when the windshield is frosted or fogged up—turning on AC for dehumidification works twice as fast as using the heater alone, but remember to turn it off afterward. Additionally, regularly replacing the cabin air filter is crucial; otherwise, the heater will blow dust into the car, which is bad for the respiratory system. Lastly, a reminder: never sleep in the car with the heater on, as carbon monoxide can accumulate easily.

[VonKarter]

The operation is actually super simple: turn off the AC, wait for the coolant temperature to rise, and adjust the fan speed. I usually wait for the temperature gauge to reach the one-quarter mark—about 3 minutes after starting the car—then turn the temperature knob to the red high-temperature zone and press the fan speed button directly. There’s no need to touch the AC button at all because it only controls the refrigeration compressor, while the heat for warm air comes from the engine cooling system. To adjust the temperature, simply turn the knob, or press the temperature +/- buttons for automatic climate control. The only exception is when encountering sudden fog—press the MAX defrost button first (most cars will activate the AC), and turn off the AC immediately after the fog clears. Don’t keep the recirculation mode on for too long; switching to fresh air mode after half an hour is the safest. Remember the three basic steps for using the heater in winter: wait for the coolant temperature to rise, turn off the AC, and adjust the fan speed.

[BellaAnn]

Unlike summer when you must press the AC button, winter operation is completely different. Summer cooling requires the compressor to turn refrigerant into low-temperature gas, but winter heating essentially recycles heat from the engine's 90°C coolant. The operation only requires three steps: wait for the coolant temperature gauge to approach the midline before turning on the fan, rotate the temperature knob to the red high-temperature zone, and keep the AC button off throughout. The principle difference is like a refrigerator and a heater—cooling relies on machine operation, while heating utilizes waste heat recovery. The only commonality is that AC can be used for quick dehumidification during defogging. Actual tests show that turning off AC and using heating in winter can save 0.8 liters of fuel per 100 kilometers. Remember to check the coolant level monthly, as low levels can cause insufficient heating. Turn off the heater before parking to allow the air ducts to dry and prevent mold.