This is the second time this happens to me in hot weather Outside temp. 35C +.
After driving for over 30 mins on highway with Airconditiong set to auto at 23.5C front with rear turned on from the front control panel . And the fan running on low automatically with nice cool cabin temperature. Suddenly the rear fan goes to high speed by itself. I could only hear the sound of the blower, nothing shows on the front or rear control panels.
If I turn off the auto the fan speed drops back to normal. Once I hit auto again it goes back to highspeed.
I was wondering if this has anything to do with the hybrid battery temperature, or is there something wrong in the rear temperature sensor?
the rear has an auto choice also, I believe. if you want it on a fixed speed, you can adjust it to the desired speed and next time it will turn on that speed. auto means adjusting to ambient temperature to cool the cabin as fast as possible hence the loud sound.
When the rear is set to auto (panel off)it is set and controlled by the from panel control. So there is no reason for the sudden increase of rear fan speed only when the car has been running for over 30 mins and the interior ambient temperature is cool enough and comfortable.