can someone explain to me how this circuit work, tired searching but never got the answer i need. car is 91 with AC

my understanding is that theres power going to the sensor on hte back of the block and when it gets hot it opens and flows power through, now this is where i dont know. does from the sensor on the back of the block does hte wire go straight to the fan or does it go through a relay, if so where is that relay exactly not like oh its on the passenger side but where and what relay it is exactly

but my problem is that my rad fan doesnt come on at all for hte radiator but it does come on for the ac. and my ac fan doesnt come on at all but i already know its the motor for the ac fan

 

not the red, red is with out A/C

 

This is what you do:

1) Go to autozone
2) Pick up 1 relay for foglights(30amp), 30amp fuse, wire, other needed goodies
3) Hook it up with a switch to BOTH fans
4) enjoy

I'm running NO temp sensor, just a gauge and on the interstate today I never went above 160degrees and usually in town I max out at 180, and my thermostate is rated at 180.