Unless I haven't done enough reading, but I've noticed everyone talking about the radiator fan coming on during high temps and after turning off the car.
Well I've never heard my radiator fan come on as long as I've own my car which is 4 years now. I live in the SoCal area, drive through rush hour, park the car in the garage and maybe decide to wash the car and I've not heard the fan come on.
Presently my only complaint is that the a/c is not blowing cold air just cool air.l

 

I had never heard mine turn on either even after a 100* day in the summer with AC after driving hard.

However the other night in 70* weather it turned on for the first time after driving medium hard when the car was off...weird!

 

It sounds that you have a slow coolant leak and hopefully nothing to worry about. Your story sounds very similar to other stories I've heard with the same problem.

The coolant tank cap on most R53 models is known for having a bad seal => causing leakage. I believe there was even a factory recall for some of the 2002-2005 models because the failure was so common. Look at the tan brown coolant tank under your hood and see if you see any dried antifreeze lines on the side of the tank.

If so, simply add some 50/50 antifreeze mix and get the fluid levels back up to the factory spec line marked on the tank.

My 2003 MCS had this problem several years ago when it was still under warranty and I got a newly designed tank and cap and it hasn't leaked since.

But then this past year (after 6 years of ownership and 70,000 miles) I noticed my radiator fan was coming on again after I turned the car off. This time I discovered the cause was a leaking radiator and had to replace the entire unit .

And for your A/C not blowing cold air, join the club. True for all cars, A/C seals begin to age and slowly deteriorate over time. The rubber begins to harden and crack due to many heat cycles and normal wear and tear. Go to a local trusted car shop and see if it needs recharged, or have them run a leak test and see where its leaking and what parts/seals are worn. It shouldn't cost you a fortune.