Why is it more fuel-efficient to drive at high speed and turn on the air conditioner?

The general manual air conditioner (non-variable displacement air conditioner compressor) only adjusts the air volume, that is, the speed of the fan, which has nothing to do with the compressor. As long as the air conditioner is on, the compressor has been running at full speed, so there is no problem of saving fuel. Of course, the air volume is large, the power consumption is large, and the oil consumption is also large in theory, but the actual difference is very small and almost negligible.

Temperature adjustment is just to choose how much hot air is mixed into cold air. In fact, the temperature inside the car can't reach the condition of stopping the compressor.

The principle of automatic air conditioning (non-variable displacement air conditioning compressor) is basically the same, except that an automatic temperature controller is added, which can automatically choose whether to blow "pure cold air" or "cold and hot mixed air" according to the difference between indoor temperature and set temperature, and set the fan air volume. So the setting has little to do with fuel consumption.

At present, the adjustment of the new variable displacement air conditioner is very particular. The refrigerating capacity (power consumption) of the compressor is related to the temperature you set. At this time, if the temperature is set relatively high, the fuel consumption will be low.

Therefore, if your car is equipped with a variable displacement air conditioning compressor, then you have room to save fuel. Otherwise, how can you turn on the air conditioner? As long as the air conditioner is turned on, no matter how it is adjusted, the difference in fuel consumption is very small.

Turning on the air conditioner itself is a process of oil consumption, and its purpose is comfort, not fuel saving, to achieve the purpose of comfort. At this time, the method of turning on the air conditioner is the best. In order to save, only comfort is sacrificed.