While I am not a Mazda tech I am a Volvo tech and we have this in our higher end cars.
Volvo refers to it as "afterblow" and it is to clear out condensation from the evaporator housing to prevent musty odors in the airbox. It is likely that the guys at the dealer may not know about it because it is a Volvo function that has found it's way into other Ford products and the CX-9 is heavily integrated into the latest generation of Ford family cars.
I'm not saying 100% that is what is going on but I'm willing to bet money on it.
BTW, my 2000 S80 (volvo) has that feature but it was only last summer that my wife noticed it. It only works when certain drive criteria have been met so it will not happen all the time.
Just my .02cents.

 

I've been wondering about this problem, in spite of not being a CX9 owner. This makes the most sense of any explanation I have heard of so far.

Owners, try running the A/C system, or defroster (A/C automatically turns on) on a regular basis and see if that seems to be when the symptoms occur.
Does that seem like a reasonable way to test this theory, and makes some sense, SB?

 

The criteria used by Volvo involve outside temp, overall runtime and time with AC on as well as the amount of time the fan was on and the AC off before the car was shut off. Unfortunately they don't release the logic so I don't know exactly what conditions set it off, but a good drive with the AC or defrost on a warm day should do it.
It also may not come on right away, but later in the day or even the next day.

 

Scatterbrain, I think you have something there! It was raining the day this started I did have the defogger on but I only drove for about 15-20 minutes though. I do use my A/C quite alot in good and bad weather even today, so far the fan blower problem has not returned.

 

Just remember that it may be doing it when you are not around too. I've walked out to my car and had the fan running long after parking it.

 

I joined this forum today because the same issue is happening on my CX-9.

Here is something that I was able to produce that may give us some more clues.

While I was trying to figure out what was happening, I left the lights on and turned off the engine. The fan came on - as it had been doing, but I was able to cause the fan to shut off when I turned off the lights. If I turned the lights back on - the fan came back on and vice versa. I have not been able to replicate this every time - it may have been related to having the car door open as well. But, it makes it seem like it is related to some issue with warning signals when the car is turned off - like your key is in the ignition, or lights left on - or something.

Its not consistent. And, of course, it just stopped this week - before I got to the dealership. Mine is a 2008 CX-9 - and it started about a month ago.

If anyone is able to get traction with the dealership - I would appreciate hearing any details.

Barry Hall

 

just bought a 2008 cx-9 yesterday and when i got home, without having had the ac or defroster on, this same problem happened to me. anyone have any update on this issue?

 

Any solutions or answers from anyone regarding the compartment fan blowing while car is off? Mine just started today out of nowhere. I called the dealer and the service tech told me it could be the relay???? Have not brought it in just yet! Wanted to see if anyone else found the real problem and solution. BTW I have not used my heat or AC in several day and neither was on today.

well today i tried the clean filter.....did not work and now the rear control blower goes on when it is not even turned on. Electrical in someway maybe????????????????

 

There's a TSB out on this, check with your dealer.
TSB: 07-008/09

2007-2009 CX-9 - BLOWER MOTOR STAYS ON AFTER KEY OFF

 

Hi CX9gal,

I had the same issue with my CX-9 and it turned out to be a heater relay. Seems like its a common problem with the CX-9's.

Good luck!

Cheers,

Richard