Should the AC be turned on when using the heater?

[LeGiselle]

There is no need to turn on the AC when using the heater, because the AC button is only the cooling switch for the car's air conditioning. When the air conditioning is turned on, pressing this button activates the air conditioning compressor, which then blows cold air. Therefore, the AC button should not be pressed when using the heater. The correct way to use the heater is to first warm up the engine, wait for the engine's water temperature to rise, and then turn on the heater. At the same time, set the air conditioning to external circulation, wait for 3 minutes to expel the cold air inside the car, and then switch to internal circulation. This can quickly increase the temperature inside the car. The car air conditioning is used to adjust and control the temperature, humidity, air cleanliness, and air flow inside the car cabin to a suitable state.

[VonEmilia]

In winter, turning on the heater usually doesn't require pressing the AC button, because the warm air mainly comes from the engine's heat circulation and is blown directly through the vents. Having driven for ten years, I've found that turning off the AC in most cases saves more fuel, as the heating system itself can warm up the cabin. If the air feels dry or the windows fog up, you can increase the fan speed or use the recirculation mode to reduce the entry of cold outside air. Some people mistakenly believe that the AC must be on for heating, but that's not the case; the AC's primary function is cooling and dehumidifying, which is only useful in summer or for defogging. I remember once when the temperature dropped suddenly, I turned on the heater without touching the AC, and the cabin warmed up quickly without any noticeable change in fuel consumption. I recommend trying just the heater in winter—it's simple, efficient, and energy-saving. If fogging becomes a serious issue, consider manually turning on the AC for a few seconds to dehumidify, but avoid keeping it on all the time. Overall, adjust based on actual driving conditions for the best results.

[Kendra]

I usually decide whether to turn on the AC with the heater based on the weather. If it's cold but dry, I just turn on the heater directly without touching the AC button, which reduces engine load and saves fuel on long trips. If it's rainy or humid and the windows tend to fog up, I briefly turn on the AC to remove moisture and improve visibility. Honestly, using the AC too much in winter makes the air drier and colder, which is uncomfortable. Once, I forgot to turn off the AC and drove for dozens of kilometers—the car was warm but stuffy. After breaking that habit, it became much more comfortable. The heating system is very efficient, directly utilizing the engine's waste heat—don’t waste this feature. Also, check the cabin air filter regularly to ensure smooth airflow. Basically, I recommend trying the heater first and adding the AC only if fogging becomes an issue.

[DiJoshua]

It's generally more economical not to turn on the AC when using the heater. From a cost perspective, running the AC increases engine load and fuel consumption, especially in winter when fuel usage is already higher. The heater itself operates through heat recovery, which helps save on fuel costs. After years of driving a small-displacement car, I've learned a fuel-saving trick: set the heater to medium temperature, turn up the fan speed, and simply turn off the AC. If there's slight fogging on the windows, just wipe it with a towel or switch to external air circulation—no need to keep the AC running constantly. The car's heating system works perfectly fine on its own; don't let it compete with the AC.

[LeBentley]

Consider safety when using the heater and avoid blindly turning on the AC. The heater alone can provide warmth, but it's wise to briefly activate the AC for dehumidification when window fogging obstructs visibility. I've encountered several foggy days where not using the AC resulted in slow defogging, but turning it on for a while quickly cleared the windows. Avoid setting the heater temperature too high to prevent overly dry and uncomfortable air. Additionally, prolonged use of the AC system may increase the risk of malfunctions. Simple rule: primarily use the heater, and assist with the AC only when needed for defogging.