Chevrolet Repair: radiator cooling fans, coolant temperature sensor, vehicle speed sensor

Question
My 1996 Caprice 4.3 has two electric cooling fans.  How does the elec. distribution to the fans work?  I know one is primary and one is secondary.  When are they both on as opposed to only one of them.  The schematics in the Haynes manual I have, only trace back to the "PCM".  The prints don't show what sensors control what and under what conditions the fans activate separately or in unison.  Can you explain it to me?  Thanks  

Answer
Dan, I'm gonna cheat for this answer.lol. here is you answer right off Alldata.Saves typing.

This two fan system is PCM controlled by inputs received from the engine coolant temperature sensor, vehicle speed sensor, and the A/C system. The PCM commands the primary cooling fan On when engine coolant temperature exceeds 225°F, A/C head pressure is above 225 psi and when certain diagnostic trouble codes are set. The primary fan is commanded Off when engine coolant temperature drops below 217°F, or A/C head pressure drops below 180 psi.

The secondary cooling fan is commanded On when the engine coolant temperature exceeds 232°F, A/C head pressure is above 248 psi or certain diagnostic trouble codes are set. The PCM commands the secondary fan Off when engine coolant temperature drops below 224°F, or A/C head pressure drops below 203 psi.

Hope that gives ya what ya need.