I noticed wasn't running at full speed, but then it was running normally, at the speed I selected. I do have the automatic AC. Sometimes, if I turn off the fan, it won't restart until I restart the car. I read online about the possibilities, I checked the battery with a scanner and also my laptop, it's only a year old, and is OK, I also changed the speed selector that I have sitting for few years, it didn't fix it. I also read the errors and cleared them, not really descriptive.
I read in one of the forums that a person found a work around: switch to "auto", move the fan speed up or down, and then deactivate the "auto" function. I tried it and it seems to work.
This is what I think: The fan is OK, because it can go up or down, just not consistently. The speed selector is OK too, I had installed another one because it had the heating seat logos and it looked better, so I switched to the original that came with the car, that cleared an error too. It seems the blower resistor/controller is working too, because I can change the speed.
There is a box that I found looking at the diagrams, it's the "control unit air conditioning system", part number 64119874189, it sits next to the blower fan.
I'm posting here to check if somebody had this problem and how it got resolved.

Send me your thoughts.

 

I will start with I can't help you with any solutions, only thing I can offer is how my '17 seems to work.

I never use 'auto', as I don't care for how it operates, so I work everything manually. Even though I work everything manually the system controller still 'fiddles' with the system, mostly noticeable with the A/C and fan operations. This has been this way since day 1 when I picked the car up back in 2016 for reference.

I can turn my A/C off via the dash button and only sometimes will it actually shut off. Most of the time it will take 5-10 minutes to finally decide to follow my button command. I always shut off my A/C before turning off the car, then select it back on after 1-2 minutes when I get back in and start the car. I can say that 90+% of the time, the car restarts with the A/C blowing full cold w/o indicating the A/C is on via the button. If I leave it off and head off driving, the A/C will stay on for some random amount of time then eventually shuts off. I have had the system also shut off the 'manual' recirculation setting on me as well, not all the time but seemingly random. I know I am not loosing my mind as my wife has noticed it shutting off the recirculate setting as well.

On the fan speed, that is where the control system seems to decide just when it will actually bring the fan speed up to my manual setting. This happens with heat and A/C, doesn't seem to matter. Sample scenario is you get into your car in the summer and it is HOT in there. Turn on the A/C, set fan speed to 5 out of 6 to cool things off. Fan turns on at a 'decent' speed, but not as much as expected. Drive off an ~2-3 miles down the road the fan speed very noticeably comes up to what seems to be full speed for another 3-5 miles then it dials it back down to what you would expect to be fan speed 5, which is between the startup speed and 'full blast' speed settings it just cycled through. From there, all fan speed settings change according to the speed selected.

It is if the system controller is running some form of control algorithm in the background that still overrides the manual settings till some certain parameters are met. It can be a bit frustrating at times, but I have learned to be able to ignore its quirks. Hope this info helps in some fashion.