pmw fan controllers

[sjaroslo]

That works fine for the coolant temperature bit, but the A/C makes it trickier. In that case the DCC controller will turn on the fans when it senses the A/C running, even if the vehicle is cruising. I don't know about the Painless part, but I'll bet it will do the same. IOW, most of these controllers just have a simple A/C override without taking vehicle speed into account.

Actually, John, it looks like they covered this. From the F5 manual:

"Note:If vehicle has the A/C compressor running but is also traveling above the vehicle speed set point the F5 controller will not engage the cooling fan. This is because when a vehicle is traveling at highway speeds the air moving across the A/C condenser should be adequate for the heat transfer required by the condenser."