Is there any harm in turning on the AC while using the heater?
2 Answers
The downside of turning on the AC while using the heater is increased fuel consumption, and activating the AC can also reduce the effectiveness of the heater. In fact, there is no need to turn on the AC switch when using the heater because activating the AC starts the air conditioning compressor, which provides cooling. The correct method to use the car heater is as follows: 1. After starting the car, wait approximately 8-15 minutes until the water temperature reaches normal operating temperature, then you can turn on the heater. 2. Adjust the air circulation mode to internal circulation. 3. Switch to the heating mode, which may be indicated by a red zone or a sun symbol depending on the vehicle. 4. Do not turn on the AC switch, as the heater utilizes the car's own heat cycle, saving energy. 5. Adjust the air conditioning to a suitable setting and direct the airflow as needed. 6. Generally, the heater airflow should be directed forward and towards the feet, while the cooling airflow is usually directed forward.
As a veteran driver with over a decade of experience, I must say there are indeed drawbacks to keeping the AC on while using the heater. The main issue is that this activates the air conditioning compressor, which puts an additional load on the engine and definitely increases fuel consumption. Moreover, the compressor doesn't operate efficiently in low temperatures, and frequent activation can accelerate mechanical wear, potentially leading to premature failure of the AC system in the long run. However, in humid conditions where the windows fog up severely, briefly turning on the AC for dehumidification can be quite effective—in such cases, it's necessary to use it. Normally, once the engine coolant reaches operating temperature, the heater alone provides sufficient warmth without needing the compressor's assistance. I recommend developing the habit of checking whether the AC light is on when using the heater and turning it off whenever possible to save on fuel costs.