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

[VonJessica]

You don't need to turn on AC when using the heater in the car. The AC button is the cooling switch for the car's air conditioning. The method to turn on the heater is: 1. Start the car and wait until the water temperature rises to the normal level, then turn on the heater; 2. Set the air conditioning circulation mode to the internal circulation mode; 3. Switch to the heater mode; 4. Adjust the air conditioning level to a suitable position. The components of the car air conditioning system include: 1. The air conditioning cooling system; 2. The heating system; 3. The air distribution system and control system. The functions of the car air conditioning are: 1. Adjust the temperature, humidity, airflow direction, and speed inside the car, and improve the air quality inside the car through the filter; 2. Provide a comfortable riding environment for passengers, reduce travel fatigue, and create good working conditions for the driver.

[JocelynMarie]

Actually, you don't need to press the AC button specifically when using the car's heater. I used to think it was necessary until a mechanic explained the principle to me. The car's heating system utilizes heat generated by the engine, which is transferred to the air conditioning ducts via coolant, consuming no extra fuel at all. Turning on the AC activates the compressor, which is designed for cooling and dehumidifying. In winter, using the AC might actually worsen window fogging because compressor operation condenses moist air. If you're in AUTO mode (automatic climate control), the system may occasionally engage the compressor to prevent fogging, which is acceptable. But remember when manually using the heater: turning off the AC brings more comfort and saves fuel. If you notice window fogging, simply direct high airflow toward the windshield.

[RubyAnn]

I've personally tested this! Last winter, I conducted a special experiment: driving 50 km with the AC on consumed 0.7 liters more fuel than without it. The car's heating system works differently from household heaters. The engine operates at 80-90°C, and this heat can be recycled. Turning on the AC forces the compressor to work, not only increasing fuel consumption by about 6% but also causing throat dryness due to alternating hot and cold air. My advice is to turn the temperature knob to the red zone and set the fan to level 2—that's warm enough. Only press the AC button when you need to defog the windshield on rainy days. Otherwise, it's really unnecessary. Remember, a green light on the AC panel means you're burning extra fuel!

[VanKevin]

No need to turn on the AC at all—this is a common misconception among new drivers. Think about it: the engine compartment gets extremely hot, so transferring that heat into the cabin via coolant is the most efficient way. My car has been running for ten years, and the heater control is just a simple knob turn below the screen. Just remember to engage recirculation mode to speed up warming, then switch to fresh air mode once the cabin reaches the desired temperature. Accidentally turning on the AC not only brings that stale air-con smell through the vents but also triggers the compressor's noticeable humming sound. If you spot the AC indicator lit on the dashboard, press it off immediately!

[DiCharlie]

When it's extremely cold just after getting in the car, I turn on both the AC and heater for 20 seconds to quickly warm up, then immediately turn off the AC. The principle is simple: although the compressor blows cold air, it instantly reduces air humidity, and when mixed with warm air, it can raise the perceived temperature faster. However, keeping the AC on continuously can cause the evaporator to frost over, which in turn reduces heating efficiency. Last week, someone in the car owners' group complained that using the AC with the heater caused their fuel consumption to skyrocket to 11 liters per 100 km. The best practice is to wait until the coolant temperature gauge reaches the midpoint before turning on the heater, directly turning off the AC and switching to external air circulation, with the temperature set around 25°C for optimal comfort.

[VonEmersyn]

As a car owner in the southern coastal area, I've summarized a trick: turn on pure warm air and turn off the AC on sunny days, and turn on the AC + external circulation on rainy days. Because air humidity determines whether the compressor is needed for dehumidification. Once during the humid season, I didn't turn on the AC, and the windshield fogged up instantly, almost causing an accident. In fact, the car's air conditioning system is very smart. When you set the temperature to the highest (like setting it above 28°C in my car), many models will automatically turn off the compressor. Pay attention to the air vents: the air from pure warm air is drier, while the air with AC has a slight medicinal smell. Finally, I remind owners of older vehicles to change the air filter frequently to avoid health issues caused by odors from the warm air.