The a/c fan speed in the automatic mode has been fluctuating from one speed to another more frequently than usual. The speed will increase and than decrease without me adjusting the temperature on a more frequent schedule than it had before. Does anyone know why this is happening and/or what sensor might be affecting this issue? This has become somewhat annoying. Thanks all.

 

That's interesting. Maybe the efficiency has degraded over time. I never use auto. Well, just for outside or recirculate and even then I will keep it in recirculate often in city driving.

 

I keep mine in recirculate most of the time as well, but it is still in the automatic mode. I have Nav and in order to change the speed of the fan I would have to go into the climate control of the screen to change it which of course is a pain.......therefore I'm usually in the auto a/c mode.

 

Yeah, it's a personal preference. I prefer to change the fan speed myself. It annoys me if the system is doing it for me. Funny.

 

In auto mode, the blower speed is determined by the "Duty Ratio", which is the percentage of time the A/C compressor is "ON" within one On/Off cycle. One way to prove that your blower is functioning properly is to adjust your temperature setting up (hotter) which will reduce the compressor run time and keep the blower at a slower speed, or turn the temperature down to extend the compressor's run time which will keep the blower at the faster speed.

 

Thanks for the comprehensive explanation. Yes, the fan speed does decrease when the temp is raised and increase when it is lowered. It has always done this flawlessly. What I now see as problematic (and has not occurred previously) is that even at one set temperature on Auto, the fan speed is constantly going faster and slower, faster and slower regardless how long I keep the temperature AT THE SAME SETTING I've had the car for over 4 years and it is only doing this now.

 

Let's try this... On your next drive when your blower begins to change speed frequently, drop the temperature setting by 3 degrees and see if the blower stays on the faster speed. It's possible that the ambient temperature makes your compressor to cycle on and off so that your duty ratio is too close to the switch point. I really don't think your blower motor is failing.

 

Thanks rkw77080........ Actually, I never thought of this as a blower motor failing problem, but more of some kind of sensor misbehaving. I'll certainly give your suggestion a try tomorrow and will report back with my findings. Thanks again for your valuable help.