Auxiliary fan question - 300CE

[rgnprof]

I think I have read every aux fan thread, but I have a slightly different question. My low and high speed fans work and come on appropriately - but what turns off the low speed fans?

It has been hot here and if I turn on the A/C the low speed pressure circuit kicks in pretty quickly - but if I turn the A/C off the fans stay on. If I shut the car off and then just turn the key on, the fans start running again. It is not the high speed - car wasn't close to 105-107 C and fans were clearly running at the low speed.

Any ideas?

ryan