Eric, actually I do not believe it is a straight line from the A/C compressor turns "on" and the fans ( 1 & 2 ) are turned on.
Page 6B-5 lists these inputs as having influence on fan operation:
A/C condenser pressure, coolant temp, oil temperature, vehicle speed, TPS signal, rpms, and ECM status are all listed in the FSM as having an effect on fan operation.
I know if my coolant temp is up around 220+ and I'm stopped in traffic and I turn on the A/C the secondary fan comes on to join the primary. But if I turn on the A/C at idle in open loop ( cold coolant less than 140* ) neither fan runs.
Tom