Yes, it does the 10-second delay start-up, then spools down and restarts when the temperature rises. At least that's what I observed this past summer when I installed the electric main fan replacement. I haven't tested the Aux fan since then.

It seems to work as it should, because with the A/C on, the coolant temperature (that I monitor on a Torque Pro display) rises fairly slowly until the aftermarket fan kicks-in at around 175F.

My two small General Motors cars, with Ecotec 4-cylinder engines, have electric fans from the factory, that start up automatically when the A/C is switched on (or when the coolant reaches 217F, if the A/C isn't being used). I like the BMW system better, because the Aux fan gives you an indication if it's still functional, before it gets too hot (and if your/my main electric fan is not working).

__________________
01 BMW X5 E53,3.0i-5L40E, 7/13/01
topas-blau,Leder-grau,"resto-project car"

Here:
14 Lexus ES350,3.5L-U660E
09 HHR Panel,2.2L-4T45E
04 Chevy 2500HD,6.0L-4L80E
98 GMC Sierra 1500,5.7L-4L60E

Gone:
66 Chevelle Malibu 2dr ht.,327>441c.i.-TH350>PGlide/transbrake
08 Cobalt Coupe,2.2L-4T45E
69 & 75 C10s,350c.i.-TH350
86 S10,2.8L-700R4
73 Volvo 142,2.0L-MT4
72 & 73 VW SuperBeetles,1.6l-MT4
64 VW,1.2l-MT4
67 Dodge Monaco 500 2dr ht.,383c.i.-A727
56 Chevy 210 4dr,265c.i.-PGlide