Thanks, Arthur, for the suggestions. My high-speed fans do work. I probably obsess a bit about coolant temperature (but then, judging by the number of posts on this, I'm not the only one). Donnie had posted a reply a couple weeks ago to someone who felt his engine was running hotter than it should (though still below 100) and Donnie recommended checking out the preresistor and its wires since he'd replaced many of them. You're absolutely right, the low-speed fans come on when AC pressure is high, so I think Donnie's point was that there are circumstances when ambient temps are not high enough that coolant temp will trigger the high-speed fans but AC pressure would be high enough to switch on the low speed fans, which in turn would lead to cooler engine coolant temps in stop-and-go traffic.