Jimmer350

Due to the weather yesterday was one of the first times I've opened my sunroof. My climate control was set on auto where it always is and I used the tilt feature on the sunroof to crack open the back of it a little. As soon as I did that I noticed the fan speed kick up quite a bit. It only did this above 50ish KPH (35ish MPH) and the more I sped up the faster the fan went. If I slowed the car down to below 50KPH it would return to normal. It ONLY did this when the roof was open - not if it was closed. At first I thought I was just hearing wind in the cabin from the roof being open but after closing and re-opening several times I realized in fact the climate control fan was speeding up and slowing down with my speed when the roof was open. When I closed the roof and didn't change my speed the fan would slow down to normal again. The display never showed any change in fan speed.

Has anyone else noticed this? Is this normal - maybe a feature to keep the temp setting while a window is open. I do not have nav.

Thanks!

teracon

This has happened to me on many cars. While I am not an engineer, I would guess that the drag that the car is producing is somehow sucking the air out of the car cabin through the sunroof. This would also happen if you roll down your window. Conversely, if you were to place the setting on "circulation" mode, the air from the vents would cease.

A way to check this is to first turn on your a/c for several minutes. Make sure that the setting is on "outside" air. Turn off the a/c and proceed to roll down your window/sunroof. Drive as normal. You will feel cold air coming from the vents. This air should remain cold for a few minutes then return to the standard air temperature.

L-Tuner

I'm not sure if there is an electronic feature that does that, but I can give another reason why that would happen. The faster you travle with the sunroof open, the more loss of cabin pressure you will suffer thus leading to a decrease in cabin temperature. That will result in the fan working harder to try to compensate. If you are driving slower, There isn't such a rapid drop in the remperature thus leading to the fan nothaving to work as hard to keep the temperature up.

Let me know if you understood that. I worded it as best I could.

L-Tuner

you beat me to it Teracon.

Jimmer350

That's what I was thinking but just wanted to make sure this is an actual feature.

Why wouldn't the display show the fan speed as it changes??? It does every other time.

mcfly

Because the cabin pressure is dropping, the fan has less drag and is speeding up. The computer isn't telling the fan to move faster, physics is. Hence the display isn't changing.