Hello no expert but I believe it is because the actual temp inside the car is higher or lower than what is set onthe system and if in auto mode, will look to match the set temp as quickly as possible hence high fan speed in order to circulate air as quickly as possible, fan slows down once that is matched. Hope this helps.
yes, auto function needs to be disabled to avoid this. The purpose of the auto function, as DBQ3 has stated, is to bring the inside of the car to the set temperature as quickly as possible, and keep it there. So if the car is initially very hot (ie left standing in hot sun) then the fan will be on full initially and gradually slow down as the set temperature is approached. You cancheck this out by increasing theset temperatureuntil the fan slows down (eg if the fanslows down when the selected temperature is increased to, say, 26C, then that istheactual interior temperature).The same thing happens in winter if you get in a cold car, and the interior needs to be heated, though bear in mind the fan itself will not go to maximum until there is sufficient water temperature to provide heat.I do not understand when you say the AC fan increases along with engine speed. Is this something that is just coincidental with the above explanation, or something else entirely?
It's indeed not speeding up when your speed goes up, but speeding up when it has enough energy. It's a behaviour lik in all my previous cars.What I find a pitty is that the sound of the car radio goes up when speed goes up, but they didn't think about the sound of the AC overpowering the radio. I don't understand why the radio doesn't go up when the AC is on a noisy full power.
thanks for all your response, but for my car, is really the case, even after we had been driving for quite some time, and the temperature in the car has reached the set temperature...but when speed up the speed, the fan speed increase too..