correct. just not immediately at startup after its been sitting for a while. like overnight.

fire it up and watch it with the AC off. The system self tests the aux fan periodically even with the AC fan off. While it's idling, after a period of time (sorry I'm not sure how long) the computer will spin the fan up to speed for ten to twenty seconds and then stop. If it's not doing that, even when cold it points to a possible aux fan problem.

Aux fan problem only at startup? I mean I’ll change it out in the next couple weeks. I hate intermittent problems :) I’ll post an update then

Compressor is failing. I went thru this with mine when I bought it. The time needed will get longer. Mine was up to taking an hour or more of running the motor before the ac would blow cold.

This explains it all.

BMW X5 Air Conditioner Compressor | Crowz Nest

Welp. That’s what I needed. Doesn’t explain my aux fan not coming on at startup though does it?

Try using a stick to coax the clutch disk to engage. Be careful, the disk might snap in and the aux fan start as soon as you touch it.

I'm not aware of the aux fan always running with AC just at a colder temp. The AC compressor has two levels of compression yours may only be working on one I've heard of hacks that make it stay in one to extend the lifespan.

It's quite obvious when the compressor kicks on so do a little testing to see if it comes on right away when AC button is pressed.

It may only come on after aux fan does come on i haven't tested it myself to know

Its possible the aux fan would of delayed about coming on while the compressor wasn't putting out any pressure. I cant answer this though because my aux fan was bad when I bought mine.

On a side note though the aux fan isn't "needed" to make the ac cool. It helps, its a good thing for it to be working and all but its not needed.

So the aux fan not running isn't why the ac wont cool.

As I mentioned in the link I posted if the compressor is running and it isn't cooling until the vehicle runs for x amount of time then suddenly goes to cooling fine its the compressor. No ifs ands or buts.

AC Takes forever to blow cold.
 

That's solid advice. I'm about to get in my car and I'll check if aux fan kicks on right away. The new scanner I have (foxwell nt510) will tell me the evaporator temp and manually engage the aux fan and the ac compressor. very helpful.

I just did a test: when engine was just started and cold, when I first engage the AC I can hear the compressor kick on nearly instantly, about ten seconds later the fan blips and turns maybe 1/8 of a turn then about 15 seconds later the aux fan comes on SLOW. Maybe the fan's slow function isn't working and ac won't stay on until it kicks in high or else it's the low compression mode of compressor shot look into how to jump out that setting and force high compression it's your one shot before replacing compressor if that's the problem.

The compressor and its functioning aka running doesn't care if the aux fan went on a vacation to Hawaii. You can remove the aux fan and leave it at home and the compressor will still run and the a/c will still cool. The mechanical fan will move enough to handle the high side pressure limits. Now if it was cooling and you came to a stop and it stopped cooling very good then the aux fan or the mechanical clutch on the main fan might be bad.

But the wont cool till x amount of motor run time is a bad compressor. No if ands or buts. The time needed for the motor to run increases the worse off the compressor is.

2 to 5 minutes is the early stages. 30 minutes or so is mid death. 1 hour plus is on its last legs.

Again if the ac wont work when you first crank up but starts working fine later on and keeps working till the x5 is left sitting for awhile (usually an few hours and definitely over night) its the compressor.