Hi everyone. This is strange as my first post, especially considering I don't own an X5 at this stage, but I have an idea on what may be happening. To set the scene a few weeks ago I took a 3.0D for a test drive and found it strange that the Air Conditioning didn't seem to be blowing cold air no matter what the temperature or "cold face, warm feet" dial was set to. Then about 3/4 of the way through the test drive it started working with a nice cold blast of air. Both the salesman and I were perplexed on why it did this.
Then a possibility hit me. When we first started the car and during the early stages of the test drive the exterior temperature display on the dash was showing around -31 deg C when it really was in the mid 20deg C range. Near the end of the drive when the A/C was working as expected the exterior temp display was showing in the low to mid 20s. It then got me thinking that the car thought it was well below freezing outside so wouldn't engage the compressor clutch to prevent freezing in the lines etc etc etc. I remember my old E36 used to disable the A/C compressor when it dropped below freezing (for real) so I thought this could be the reason in this case.

It may not be the cause of this particular problem but it may be worth checking what the external temp gauge is telling you when it doesn't blow out cold air. Worst case it will rule out another potential cause for the problem!