Checking the a/c cooling fan on a 528i

[tdm34ds]

Just a quick question to our resident e39 experts,

I've had my 528iSE for nearly 18 months now, and in all this time i've never seen or heard
the electric a/c fan in front of the radiator switch on, I run my car with the a/c on all of
the time, even yesterday in horrible traffic with the outside temp over 28C the fan didn't switch
on! and as an experiment when I got home I left the car ticking over for 25 minutes and the fan still didn't switch on. The coolant guage didn't move from it's normal position on the gauge
and the the a/c worked fine.

Is there any quick test I can do to check that the fan is operating properly?

thanks in advance