I know you have one that comes on with temp.....
the other comes on with the A/C

is there reason why you wouldn't want them to come at the same time,
since they'll both be on with a/c anyway.....

I was thinking why only use half of the radiator for cooling

 

The 2nd fan will come on if the coolant temp rises above
a certain temperature,not sure of the temp the 2nd fan
comes on at-240 degees i think.If i had a 3rd gen with
dual electric fans i would modify the wiring so both fans
would come on at the same time,triggered by a
thermostat about 10-15*above the coolant thermostat
opening temp as well as the A/C relay. With 2 fans,
A/C blower and A/C clutch all coming on at the same
could cause the ignition to cut out for an instant-if this
happens might have to modify some of the wiring.

 

If you haven't, you might check Willie's sticky.

JamesC