TRM04

It's really hot in SoCal and I've found that the HVAC sometimes doesn't turn on. I don't usually hit the off button when turning off the car so when I start it it usually starts but sometimes it doesn't and I can't figure out why. To make it even more confusing, there was one time it took 2-3 minutes after driving away and the fan turned on and system operated like normal. I've also noticed that when the fan is at higher speeds the speed isn't consistent it's as if it blows in waves. Is that normal? Any idea why the unit won't turn on at all?

To be clear, when I say it doesn't turn on, I mean the fan doesn't blow. The buttons and MMI functionality is fine.

MP4.2+6.0

Need a scan for better diagnostics. Meantime, do you have a solar roof by chance?

TRM04

I don't have access to a scan.

Yes I have a solar roof.

MP4.2+6.0

So this is more a probability/likely guess rather than definitive, but your symptoms coupled with solar roof suggest to me your basic heater blower fan is failing. Basically every time someone posts now with those symptoms, I (or someone else) ask the solar roof question. And almost invariably, it does seem car had the solar roof and then it is the heater fan, typically confirmed by later replacement and function getting back to normal. Scan might eliminate some of the guessing.

The basic issue is the solar roof causes the fan to run many more hours per day than basic driving, and apparently it just wears out. Had it happen on my 2000 A6 (C5) 4.2 with solar roof...twice over the years. It has been discontinued again as an option on the D4 A8/S8 in the past year, and I suspect it is related to reliability in part. Some have done a motor brush change, while many just change the blower out completely. There are a variety of prior posts and how to's on it if you search. It is under hood, deeper underneath the HVAC filter in the plenum area in back. Or, have an indy do it--and confirm the conjecture of what it may well be.

TRM04

Thanks I'm guessing you're more right than wrong. I've turned off the solar function for the time being. Let the thing cool down and I'm hoping I can resume operation long enough to get it to a tech. Thanks for the assistance.

Giovanni Giovino 6.0+6.0TT

easy job if you are handy with tools, see link for pictures of blower R&R.






https://www.audiworld.com/forums/a8-...ement-2847341/

ltooz_a6_a8_q7

I was going to look for JJ with a "B" post about this one and you beat me to it :-)

Cheers,

Louis