Do I need to turn on the AC when using the car heater?
4 Answers
You don't need to turn on the AC when using the car heater. The AC controls the compressor switch, while the heater utilizes the internal heat circulation of the car to maintain the cabin temperature. The method to adjust the car's air conditioning between cooling and heating is: 1. Locate the temperature button on the car's air conditioning control panel; 2. Turning towards the blue direction cools, while turning towards the red direction heats. The working principle of the air conditioning heating is: after turning on the heating function, the high-temperature coolant from the engine flows through the heater core, and the air blown by the blower passes through the heater core, resulting in warm air being blown out from the air vents. Precautions for using the heater: 1. Do not use the heater immediately after a cold start; 2. Control the heating system through the water temperature gauge; 3. Turn off the heater when parking for a long time; 4. Turn off the heater before shutting down the engine.
I always think about this question whenever I turn on the heater, because it's indeed quite confusing. The warm air comes from the engine's residual heat, which is naturally generated when the engine is running, and is blown into the car by the fan, without any need for the air conditioning compressor. So when you're purely using the heater, there's absolutely no need to press the AC button—doing so just wastes fuel without any extra benefit. However, if the windows tend to fog up in cold weather, turning on the AC can quickly dehumidify the air by removing moisture, making it a good combination at that time. Normally, if you just adjust the temperature to the warm zone, feel free to turn off the AC—it saves fuel and reduces noise. My habit is to turn on the heater first, and if the fog gets heavy, I’ll add the AC to defog, which is simple and efficient.
With decades of driving experience, I've learned that it's best not to turn on the AC when using the heater. The heating system utilizes the engine's waste heat recovery mechanism, where the compressor is completely unnecessary. Engaging the AC only wastes fuel, increases consumption, and harms the environment. Unless you encounter foggy windows during rain or snow—when the AC's dehumidification function can help—keeping the AC off in pure heating mode is the smartest choice. I always operate this way in winter, which not only extends the lifespan of the air conditioning system but also results in quieter engine sounds. Remember this simple principle: turn off the AC if you just want warmth; turn it on to prevent fogging. Also, don’t overlook cleaning the heating ducts during routine car checks to ensure the vents remain unobstructed.
The heating and AC systems operate independently. The heating utilizes waste heat recovery from the engine, while the AC relies on a separate compressor. Typically, there's no need to press the AC button when using the heater. On dry days, simply turning on the fan with heat is sufficient to stay warm. However, during humid conditions when windows fog up, the AC's dehumidifying function becomes useful—activating it helps remove moisture and prevent condensation more effectively. Through years of driving experience, I've learned that flexibly switching between systems based on weather conditions is the most efficient approach. Vehicles with automatic climate control can manage warmth settings automatically, eliminating the need to manually engage the AC. Regular maintenance of heating ducts to prevent blockages is a crucial yet often overlooked detail.
