Do you need to turn on the AC when using the car heater?

[MacAaliyah]

When using the car heater, there is no need to turn on the AC switch. Reason: The heating system in a car does not require the compressor to work for heating; it directly uses the hot air from the engine's cooling system as the heater. Therefore, you do not need to turn on the AC switch when using the heater in winter. Methods for switching between cooling and heating in a car's air conditioning system: 1. Rotating knob: Generally, the air conditioning switch in a car is a rotating knob with two ends. One end is for cooling (blue), and the other end is for heating (red), each marked with different intensity levels to adjust the cooling or heating strength. 2. Cooling: If you need to use the air conditioner in summer, rotate the air conditioning switch to the blue end and turn on the AC switch to activate the compressor for cooling. 3. Heating: If you need heating in winter, rotate the air conditioning switch to the red end without turning on the AC switch. When the air conditioning is not in use, simply rotate the knob to the off position.

[Cali]

Whether to turn on the air conditioning when using the heater depends on the situation. Normally when I drive in winter, the heating mainly relies on the engine's heat—just turning on the fan is enough, and there's no need to activate the air conditioning compressor, as it consumes more fuel and adds extra load. However, during humid and cold days or rainy and foggy weather in the south, I always press the defrost mode, which automatically activates the air conditioning's dehumidification function to quickly clear fog and improve visibility. After starting the car, if the cabin is dry, I simply set the temperature for warm air; if it's humid, turning on dehumidification makes it more comfortable. For long-term use, regular checks of the air conditioning system are necessary to avoid malfunctions. In short, it's not always required, but using it for dehumidification can significantly enhance comfort and safety.

[McPaisley]

You don't have to turn on the AC for heating. With decades of driving experience, I know the car's heating system utilizes waste heat from the engine - it's free and eco-friendly. Using the AC compressor for heating and dehumidification actually increases fuel consumption and costs. Living in the dry northern region, I simply adjust the temperature knob to enjoy the warm airflow comfortably. However, on foggy mornings, I briefly turn on the AC to dehumidify and prevent window fogging. I recommend using the recirculation button more often to retain warmth and save energy. When replacing bulbs or inspecting pipes, take a moment to check if the AC filter is clogged with dust, which affects efficiency. Regular maintenance saves money and ensures safety.

[StRichard]

The vehicle's warm air comes from the engine heat and does not require the air conditioning for heating. I usually turn off the air conditioning to save power when using the heater, as the compressor's operation consumes unnecessary energy. However, in humid environments, such as after rain, turning on the heater may cause the windshield to fog up. Activating the air conditioning for dehumidification can quickly resolve this issue. In automatic models, pressing the AUTO button may automatically control the dehumidification mode. Manual systems require operation based on the situation, such as briefly turning it on during long-distance driving in foggy areas. Regular maintenance checks on the air ducts prevent blockages and ensure optimal performance.