Herb - You're seeing normal behavior. The 123 cars use a temperature sensor on the liquid side of the a/c system to activate the auxiliary fan. I think it's set to about 60C.

When you first fire up the a/c, the liquid freon isn't nearly that warm - perhaps 35C on a nice, steamy Houston summer day. As the a/c removes heat from the cabin, the temperature of the freon on the liquid side of the system rises. When it reaches 60C - you get fan!

On my old 300D it took a couple of minutes on a hot day - maybe 3 or 4? On a cooler day - say 75F - the auxilliary fan never switched on.